GIFT  OF 
Mars ton  Campbell,    Jr 


;'">*• 


Prospecting  Colorado  Oil   Shale. 

(D.  &  R.  G.  R.  R.) 


POPULAR ; 
OIL  GEOLOGY 


BY 

VICTOR  ZIEGLER 
// 

CONSULTING  GEOLOGIST 

FORMERLY  PROFESSOR  OFGEOLGY  AND  MINERALOGY 
COLORADO  SCHOOL  OF  MINES 


SECOND  EDITION 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 
LONDON:    CHAPMAN  &  HALL,  LIMITED 

1920 


Engineering 
Library 

Copyright,  1918  and  1920,  by 
Victor  Ziegler 


ROBINSON    CO.,    DENVER. 


TO    MY    UNCLE 

LEONARD  KIMM 

THIS    BOOK    IS    GRATEFULLY 

DEDICATED 


834134 


PREFACE  TO  FIRST  EDITION 


The  following  pages  represent  an  elaboration  of  a 
number  of  popular  lectures  in  the  geology  of  oil  and  gas. 
These  were  delivered  during  the  past  winter,  in  part  at 
the  Colorado  School  of  Mines  and  in  part  in  the  City  of 
Denver,  under  the  auspices  of  the  Colorado  State  Oil  Com- 
mission. This  little  book  is  not  intended  to  be  a  general 
treatise  on  the  subject  of  oil  and  gas  geology.  It  is  not 
intended  for  the  experienced  oil  geologist.  It  is  written 
for  the  man  without  technical  or  scientific  training  in  this 
branch  of  geology.  Every  attempt  has  been  made  to  pre- 
sent in  as  simple  language  as  possible  the  fundamental 
principles  of  oil  geology,  and  to  render  these  intelligible 
to  the  layman  who  may  be  interested  in  this  subject  from 
the  practical  standpoint,  or  for  the  sake  of  making  invest- 
ments, or  perhaps  only  because  of  a  desire  to  add  to  his 
general  knowledge.  Anyone  who  wishes  to  continue  his 
studies  in  this  subject  is  referred  to  the  treatises  mentioned 
below,  or  to  the  author's  "Principles  of  Oil  Geology", 
which  is  now  in  preparation,  and  to  which  this  little  book 
is  really  an  introduction. 

I  have  not  hesitated  to  draw  liberally  on  the  literature 
of  petroleum.  Because  of  the  nature  of  the  book,  and  in 
the  desire  to  keep  it  as  free  as  possible  from  unnecessary 
material,  I  have  purposely  refrained  from  citations  and 
acknowledgments  in  the  text.  I  have  used  most  freely  the 
following  works:  Bacon  and  Hamor,  "The  American 
Petroleum  Industry"  ;  Johnson  and  Huntley,  "Oil  and  Gas 
Production";  A.  Beeby  Thompson,  "Oil  Field  Develop- 
ment" ;  Hager,  "Practical  Oil  Geology" ;  and  Cunningham 
Craig,  "Oil  Finding". 

VICTOR  ZIEGLER. 
Colorado  School  of  Mines. 
February  15,   1918. 


PREFACE  TO  SECOND  EDITION 


In  preparing  the  new  edition  of  this  work,  parts  of  the 
book  have  been  rewritten,  notably  the  chapter  on  oil  shales, 
the  migration  of  oil  and  gas,  and  on  the  anticlinal  theory. 
Much  new  material  has  been  added  along  the  more  theo- 
retical lines  of  geology.  The  principles  especially  impor- 
tant in  the  examination  of  prospective  oil  land  have  been 
emphasized  in  the  hope  that  the  difficult  character  and  na- 
ture of  the  work  of  the  oil  geologist  may  be  properly  appre- 
ciated. 

More  is  required  of  the  oil  geologist  than  the  ability 
to  map  a  structure,  and  to  recognize  an  anticline.  He  must 
have  the  broad  vision  and  mentality  to  comprehend  the 
geological  features  of  the  area  investigated,  the, engineering 
problems  and  technical  difficulties  which  must  be  faced  in 
its  development,  and  the  probable  influence  of  the  general 
industrial  and  business  situation  on  the  problem  in  hand. 
The  geologist,  to  be  successful,  must  view  these  factors  in 
their  proper  relationship,  must  recognize  their  interde- 
pendence, and  must  correctly  evaluate  their  relative  im- 
portance. 

VICTOR  ZIEGLEE. 
Denver,  Colorado. 
April  26,  1920. 


Contents 


CHAPTER   I. 

I  —  10 

THE  RISE  AND  DEVELOPMENT  OF  THE   PETROLEUM 
INDUSTRY. 

Present  Status  of  Oil  Industry  —  Crude  Oil  Prices  —  Appli- 
cation of  Geology  —  Petroleum  in  Antiquity  —  Rise  of  the  Modern 
Pet.'oleum  Industry  —  World's  Production  of  Crude  Oil. 

CHAPTER  II. 

II  —  24 

THE    COMPOSITION    AND    PROPERTIES    OF    OIL    AND    GAS. 

Elementary  Principles  of  Chemistry  —  Elements  and  Com- 
pounds—  Atoms  and  Molecules  —  Natural  Hydrocarbons  — 
Composition  of  Gas  —  Composition  of  Petroleum  —  Specific 
Gravity  —  Distillation  Tests  —  Miscellaneous  Properties  —  Solid 
and  Semisolid  Hydrocarbons. 

CHAPTER  III. 

25  —  35 
THE   ORIGIN    OF  OIL  AND   GAS. 

Classification  of  Theories  —  Inorganic  Theories  —  Cosmic 
Theory  —  Mendeleefs  Carbide  Theory  —  Organic  Theories  — 
Coal  Theory  —  Plant  Theory  —  Dual  or  Engler-Hofer  Theory  — 
Processes  of  Oil  Formation  —  Causes  of  Varieties  of  Oil. 

CHAPTER  IV. 

36  —  40 
ROCKS  AND  THEIR   PROPERTIES. 

Classification  of  Rocks  —  Kinds  of  Sedimentary  Rocks  — 
Conglomerate  —  Sandstones  —  Shales  —  Limestones  —  Transi- 
tional Rocks  —  Formation  —  Stratification  —  Cross  Bedding  — 
Variation  in  Rocks— Erosion  Forms  —  Driller's  Rock  Classifica- 
tion. 


CHAPTER  V. 

41  —  51 
STRATIGRAPHIC  GEOLOGY. 

Tracing   Outcrops  —  Comparing  Lithological   Characteristics 

—  Use  of  Fossils  —  Evolution  —  Preservation  of  Animal  Remains 

—  Geologic  History  —  Geologic  Time  Divisions  for  North  America 

—  Stratigraphic  Distribution  of  Oil  and  Gas. 

CHAPTER  VI. 

52  —  60 
THE  ARRANGEMENTS  AND  STRUCTURES  OF  ROCKS. 

Dip  and  Strike  —  Outcrops  —  Folds  —  Degrees  of  Folding  — 
Nomenclature  of  Folds  —  Composite  Folds  —  Faults  —  Normal 
Faults  —  Thrust  Faults  —  Unconformities. 

CHAPTER  VII. 

61  —  68 
THE   RESERVOIRS   OF  OIL   AND   GAS. 

Sandstones  —  Tests  for  Oil  in  Sands  —  Shape  of  Reservoirs 

—  Limestones  —  Shales  —  Other    Rocks  —  The    Enclosing    Beds 
of  Reservoirs. 

CHAPTER  VIII. 
69  —  79 

THE    LAVVS   OF    MIGRATION    AND   ACCUMULATION    OF   OIL 

AND   GAS. 

Causes  of  Migration  —  Differences  in  Specific  Gravity  — 
Head  of  Ground  Water  —  Gas  Pressure  —  Rock  Pressure  —  Earth 
Movement  —  Heat  Gradient  —  Capillary  Attraction  —  Conclusions 

—  Conditioning  Factors  of  Oil  Migration  —  Laws  of  Oil  Accumu- 
lation —  Modifications  of  Anticlinal  Theory. 

CHAPTER  IX. 

80  —  86 

MAPS  AND  THEIR  USES. 

Topographic  Maps  —  Geologic  Maps  —  Columnar  Section  — 
Structure  Section  —  Structure  Map  —  Isochore  Lines. 

CHAPTER  X. 

87—  116 
OIL  STRUCTURES   AND   OIL   FIELDS. 

Structure  —  Classification  of  Oil  Fields  on  Basis  of  Struc- 
ture —  Fields  with  Folded  Structure  —  Fields  with  Monoclinal 
Dip  —  Structural  Terraces  —  Structural  Ravines  —  Asphalt 
Sealed  Sands  —  Fields  on  Domes  —  Wyoming — Rocky  Mountain 
Fields  —  Colorado  —  De  Beque  and  Rangely  —  Eastern  and 
Southeastern  Colorado  —  New  Mexico  —  Lima,  Ohio  —  Saline 
Domes  —  Volcanic  Domes  —  Fields  on  Faults  —  Fields  on  Uncon- 
formities —  Summary. 


CHAPTER  XL 

117  —  122 
POPULAR  FALLACIES  IN  OIL  GEOLOGY. 

Not  all  Rocks  Carry  Oil  —  Drill  Deep  —  "Favorable  Indica- 
tions" —  Seeps  —  Salt  Water  —  Residual  Deposits  —  Oil  Shales 

—  Oil  and  Gas  Showings  in  Wells  —  Summary  —  Divining  Rod. 

CHAPTER  XII 

123  —  141 
PROSPECTING  AND  DEVELOPING  OIL  LANDS. 

Prospecting  for  Areas  of  Petroliferous  Rocks  —  Characteris- 
tics of  the  Formation  —  Ldthological  Characteristics  of  Possible 
Reservoirs  —  Locating  Structures  —  Type  of  Structures  —  Trap 
Structures  —  Retardation  Structures  —  Structures  and  Oil  Pools 

—  Topographic     Features  —  Choice     of     Structures  —  Structural 
Characteristics  —  Relation  to   Other   Structural   Features  —  Geo- 
logic   History  —  Locating    a    Test    Well  —  Economic    Considera- 
tions—  Depth  of  Drilling — Possible  Value  of  Production  —  Ac- 
cessibility —  Transportation  Facilities  —  Operating  Requirements 

—  Legal  Status  of  Land  —  Producing  Problems  —  Objects  of  Pro- 
duction —  Spacing  of  Wells  —  Amount  of  Oil  Available  —  Flow  of 
Oil  —  Defensive  and  Offensive  Methods  —  Offsetting. 

CHAPTER  XIII 

142  — 159 
OIL  SHALES  AND  THEIR    UTILIZATION. 

Oil  Shales  —  Location  —  Oil  Content  —  Green  River  Forma- 
tion—Distillation Tests  —  Analyses  of  Oil  Shale  — Shale  Oil- 
Black  Shale  —  Canadian  Shales  —  Scotland  —  Methods  of  Treat- 
ment —  Scotttish  Oil  Shale  Plants  —  Retorts  —  Condensers  and 
Separators  —  Scrubbers  —  Shale  Oil  Refineries  —  Future  of  West- 
ern Oil  Shales. 

CHAPTER  XIV. 

160  —  166 
OIL   INVESTMENTS. 

Types  of  Oil  Investments  —  Wildcatting  —  Geology  in  Wild- 
catting  —  Producing  Companies  —  Productive  Capacity  —  Cost  of 
Maintenance  and  Production  —  Value  of  Oil  —  Location  — 
Financial  Status  of  Company  —  Hammond's  Don'ts. 


List  of  Illustrations 


Prospecting  Colorado  Oil  Shale — Frontispiece. 

Figure  Title                                              Page 

1.  Production  Chart  of  Crude  Oil  in  the  U.  S 2 

2.  Fluctuation  in  value  of  Crude  Oil 3 

3.  Map  of  Oklahoma 10 

4.  Relation  of  weight  and  specific  gravity  of  Crude  Oil 19 

5.  Specific  gravity — weight  diagram 20 

6.  Map  of  Texas 26 

7.  Map  of  Kansas 30 

8.  Distribution  diagram  of  fossil  form 43 

9.  Production  chart  according  to  age  of  rock 51 

10.  Dip  and  strike 52 

11.  Various  types  of  Folds 54 

12.  Monocline    55 

13.  Folds  represented  by  dip  and  strike  symbols 56 

14.  Normal  fault 57 

15.  Thrust  fault    58 

16.  Effect  of  fault  on  wells 58 

17.  Unconformity  in  Wyoming 59 

18.  Effect  of  packing  on  porosity 62 

19.  Lenticular  sands   64 

20.  Lenticular  sands  as  shown  on  map 65 

21.  Map  of  Agusta  and  typical  well  log 67 

22.  Effect   of   capillary   attraction 72 

23.  Gas,  oil  and  water  well  on  anticline 77 

24.  Ideal  landscape  and  its  contour  map 81 

25.  Map  and  section  of  ideal  dome 83 

26.  Application  of  convergence  maps 85 

27.  Spindle  Top  Field,  Beaumont,  Texas 88 

28.  Oil  map  of  the  United  States 89 

29.  Oil  pool  in  basin,  Oklahoma 90 

30.  Map  of  Volcano  Springs  anticline,  W.  Va 91 

31.  Idealized  section  through  Eastern  oil  fields. 92 

32.  Gas  of  structural  terrace 93 

33.  Map  of  structural  ravines 94 

34.  Structure  of  oil  sand  on  terrace. 94 

35.  Surface  structure  on  terrace 95 

36.  Oil  pool  in  lenticular  sand 96 

37.  Map  of -Wyoming,  showing  oil  districts 97 

38.  Structure  map  of  Basin  Oil  Fields 100 

39.  Structure  map  of  Greybull  Oil  Fields 101 

40.  Structure  map  of  Grass  Creek  Oil  Field 106 

41.  Sketch  map  of  Colorado 108 

42.  Saline  dome    110 

43.  Section  of  volcanic  neck 112 

44.  Section  through  a  Mexican  Oil  Field 113 

45.  Oil  pool  sealed  in  by  fault 114 


Figure  Title                                             Page 

46.  Gas  pool  at  unconformity,  N.  Y 115 

47.  Oil  pool  at  unconformity,  Wyo 116 

48.  Oil  seep  and  accumulation  down  dip 119 

49.  Dome  left  as  structural  mountain 131 

50.  Dome  eroded  into  valley 132 

51.  Section  showing  relation  between  width  of  productive 

area  and  dip  of  structure 132 

52.  Section  of  oil  pools  on  unsymmetrical  anticlines 137 

53.  Flowing  well,  Salt  Creek 139 

54.  Offsetting  .' 140 

55.  Map  showing  Western  oil  shales 143 

56.  Outline  of  treatment  of  oil  shales 144 

57.  Experimental  oil  shale  plant 150 

58.  Oil  shale  retorts 152 

59.  Bench  of  oil  shale  retorts,  Pumpherston,  Scotland 153 

60.  Bench  of  oil  shale  retorts,  Broxburn,  Scotland 154 

61.  Shale  oil  refinery,  Broxburn,  Scotland 156 

62.  Production  curves  in  wells.. .  ..164 


I.   The  Rise  and  Development  or  the 
Petroleum  Industry 

Present  Status. 

The  rise  and  development  of  the  petroleum  industry 
is  one  of  the  interesting  industrial  romances  of  the  present 
day.  Starting  with  an  insignificant  beginning  of  two 
thousand  barrels  in  1859,  the  production  of  the  United 
States  has  risen  to  a  total  of  360,000,000  barrels  for  1919, 
a  figure  so  large  that  it  is  difficult  to  form  a  conception  of 
its  magnitude.  Collected  in  one  spot  the  oil  would  form  a 
lake  six  feet  deep,  covering  an  area  of  thirteen  square 
miles.  The  value  of  the  crude  oil  may  be  roughly  esti- 
mated at  $600,000,000.  Large  as  this  figure  is,  it  does  not 
correctly  represent  the  magnitude  of  the  petroleum  in- 
dustry. Thus,  for  the  year  1919  the  value  of  the  refined 
products  will  greatly  exceed  $1,500,000,000,  a  value 
greater  than  the  combined  value  of  the  production  of  gold, 
silver,  copper,  lead,  and  zinc,  for  the  same  period.  This 
is  in  spite  of  the  excessive  high  production  of  the  last  three 
products  for  war  materials,  and  their  corresponding  high 
value. 

The  accompanying  chart  shows  graphically  the  pro- 
duction of  crude  oil  in  the  United  States  since  1859.  While 
production  has  increased  from  250  million  barrels  in  1913 
to  360  million  barrels  in  1919,  consumption  has  increased 
much  more  rapidly.  It  is  estimated  that  consumption  has 
doubled  in  the  last  four  years,  and  now  exceeds  production 
by  nearly  15  percent. 

This  excessive  consumption  causes  serious  concern,  es- 
pecially because  our  known  oil  fields  are  rapidly  nearing  ex- 
haustion. Thus  the  United  States  Geological  Survey  gives 


2     .  POPULAR   OIL  GEOLOGY. 

the  following*  estimates' iis  of  January  1,  1917,  to  show  the 
percentage  of  exhaustion  of  the- various  oil  fields: 

Ohio,  Indiana    93% 

Appalachian 70% 

Illinois    .51% 

Oklahoma,  Kansas  .  .25% 
California    26% 


/S60          IS65          U70          I07S 


Years 


Figure  1.     Chart  showing  graphically  the  production  of 
Crude  Oil  in  U.  S.  since  1859. 


POPULAR  OIL  GEOLOGY.  6 

The  total  estimated  production  of  the  United  States 
since  1859  is  four  billion  barrels;  the  total  available  sup- 
ply is  seven  billion  six  million  barrels.  At  the  present 
rate  of  consumption,  this  is  sufficient  for  only  about 
twenty  years.  As  a  result  of  this  condition  the  value  of 
crude  oil  is  higher  than  it  has  ever  been  before,  in  conse- 
quence of  which  there  has  been  intense  interest  in  oil 
stocks,  both  for  investment  and  for  speculation.  Hundreds 


Figure  2.  Chart  showing  fluctuations  in  the  value  of  Crude 
Oil  for  the  prominent  American  oil  fields.  Each  horizontal  divi- 
sion indicates  three  dollars. 


of  new  oil  companies  have  been  organized,  mostly  for  the 
purpose  of  exploiting  or  prospecting  for  new  fields. 
Another  result  is  the  elimination  of  wasteful  methods 
formerly  characterizing  the  oil  industry.  Engineering  and 
scientific  methods  are  adopted,  both  in  production  and  re- 
fining. Among  all  of  these  the  most  important  is  the 
general  appeal  of  the  oil  man  to  the  geologist. 


.       POPULAR   OIL   GEOLOGY. 

The  Application  of  Geology. 

In  the  early  days  of  the  oil  industry,  drilling  was 
carried  on  in  an  unsystematic  manner,  without  any  re- 
gard for  geological  features.  The  presence  of  salt  water, 
of  oil  and  gas  seeps,  which  experience  has  often  shown  to 
be  delusive,  were  considered  indications  favorable  enough 
to  warrant  extensive  drilling  campaigns.  As  a  matter  of 
fact,  there  was  a  marked  distrust  shown  toward  the  geolo- 
gist. This  was  not  surprising,  because  in  general  the 
geologist  followed  the  oil  man  and  did  not  precede  him. 
It  remained  for  an  American  geologist,  I.  C.  White,  in 
1885,  to  give  us  the  first  clear  outline  of  the  application 
of  geological  methods  to  the  finding  of  oil  and  gas  fields 
and  to  the  locating  of  wells.  Indeed  while  geologists  had 
been  active  before  his  day,  they  had  not  recognized  the 
fact  that  geology  could  actually  be  used  for  this  purpose. 
When  White  announced  his  discovery,  it  was  received  with 
derision  by  his  own  colleagues,  who  were  only  convinced 
when  its  practicability  was  actually  demonstrated. 

Practical  men  remained  skeptical,  and  only  the 
serious  condition  of  the  oil  industry  in  the  last  few  years, 
and  a  consequent  employment  of  geologists  in  large  num- 
bers, with  the  results  they  have  achieved,  convinced  them 
that  geology  is  indeed  far  more  important  than  the  most 
enthusiastic  thought.  It  has  been  estimated  that,  in  1913, 
only  three  geologists  were  employed  in  the  Kansas-Okla- 
homa fields.  Today,  in  the  same  field,  two  hundred  and 
fifty  are  employed.  As  a  result  of  their  labor,  the  chance 
for  success  of  wildcat,  or  prospect  wells  has  been  reduced 
from  one  in  one  hundred  and  fifty,  to  one  in  three.  Vir- 
tually every  large  oircompany  of  importance  maintains  a 
geological  staff,  the  duties  of  which  are  to  prospect  for 
new  favorable  areas,  to  locate  test  wells,  and  to  map  out  a 
drilling  campaign  insuring  the  most  economical  produc- 
tion and  maximum  yield  from  a  given  field. 

The  value  of  geological  services  are  attested  by  the 
success  of  many  new  companies  to  such  an  extent,  that  it 
has  become  generally  recognized  that  a  disregard  of  geo- 
logical conditions  is  virtually  an  assurance  of  failure. 


POPULAR   OIL   GEOLOGY.  5 

Petroleum  in  Antiquity. 

In  the  introductory  remarks,  the  petroleum  industry 
was  said  to  be  about  fifty  years  old.  Its  extreme  youth 
is  very  surprising,  because  oil  and  its  products  had  been 
known  for  many  centuries  and  were  used  long  before  the 
Christian  era.  Antiquarian  explorations  in  Asia  Minor 
and  Egypt  have  proved  that  asphalt  was  generally  used 
in  place  of  mortar  for  building  purposes.  Herodotus  men- 
tions that  the  walls  of  Babylon  and  of  Ninevah  were  so 
constructed.  According  to  the  Old  Testament  asphalt  was 
also  used  in  the  walls  of  the  Tower  of  Babel.  The  ancient 
civilization  of  the  Incas  in  Peru,  and  of  the  Aztecs  in 
Mexico  employed  asphalt  for  architectural  purposes.  The 
Old  Testament  also  mentions  the  fact  that  the  Ark  of  Noah 
and  the  woven  basket  of  Moses  were  made  waterproof  by 
an  application  of  oil.  Among  the  Egyptians,  oil  was  used 
in  embalming.  Indeed,  the  word  "mummy"  is  said  to  be 
derived  from  the  term  "mumiya",  the  Persian  for  asphalt. 
Records  show  that  since  time  immemorable,  oil  has  been 
used  for  lighting  in  the  cities  of  the  Red  Sea,  as,  for 
example,  Ras  G-emsah  and  Gebel  Zeit.  The  medicinal 
value  of  oil  was  recognized  by  the  Indians  long  before 
white  men  set  foot  on  America.  Marco  Polo,  writing  in 
the  thirteenth  century,  relates  that  the  Russians  of  the 
Baku  region,  on  the  Caspian  Sea,  drank  oil,  both  as  a 
cordial  and  as  a  medicine.  As  a  matter  of  fact,  modern 
investigations  prove  that  the  Persians  sought  the  oils  of 
Baku  centuries  before  the  Russians  occupied  the  Caucusus. 
In  view  of  these  many  uses,  it  is  perhaps  natural  that  oil 
and  gas  should  become  objects  of  worship.  Most  famous 
were  the  "Eternal  Fires  of  Surakhani",  on  the  Aspheron 
peninsula  in  the  Caspian  Sea.  Here  were  the  sites  of 
sacred  shrines  and  temples,  to  which  the  Parsees,  or  fire- 
worshipers,  conducted  pilgrimages,  recorded  as  far  back  as 
600  B.  C.  A  modern  Hindu  temple,  about  two  hundred 
years  old,  marks  the  site  of  the  ancient  shrines.  The 
"Eternal  Fires"  are  really  gas  seeps  which,  once  ignited, 
will  continue  to  burn. 


6  POPULAE   OIL  GEOLOGY. 

Rise  of  the  Modern  Petroleum  Industry. 

The  first  elementary  and  crude  attempts  at  the  pro- 
duction of  oil  on  a  large  scale  were  made  by  Peter  the 
Great,  in  1723.  He,  at  that  time,  granted  a  private 
monopoly  for  oil  production  in  the  Baku  region,  which,  it 
is  interesting  to  note,  continued  in  force  to  1872. 

The  real  pioneer  in  oil  production,  however,  was  the 
United  States.  The  first  record  of  oil  in  America  dates 
back  to  1627,  when  the  Franciscan  friar,  Joseph  de  la 
Koche  d'Allion,  described  in  a  letter  the  oil  springs  of 
Allegheny  County,  New  York,  which  were  highly  prized 
by  the  Indians.  Oil  received  only  passing  attention  in  the 
early  part  of  the  nineteenth  century.  There  was,  how- 
ever, great  interest  in  salt  and  natural  brines,  which  led 
to  the  devising  of  methods  for  drilling  wells.  The  first 
drilled  well  in  the  United  States  was  sent  down  in  1806, 
on  the  bank  of  the  Kanawha  River,  in  Virginia.  This  well 
was  eighty  feet  deep  and  produced,  in  addition  to  salt 
water,  about  twenty  barrels  of  crude  oil  a  day.  In  1820 
drilling  methods  were  so  perfected  that  it  was  possible  to 
drill  wells  one  thousand  feet  deep.  The  general  demand 
for  salt  and  brines  resulted  in  the  drilling  of  a  great  num- 
ber of  wells  along  the  Kanawha.  A  great  number  of  these 
produced  oil,  which  was  considered  obnoxious  and  waa 
permitted  to  flow  into  the  river.  From  this  practice  origi- 
nated the  name  of  "Old  Greasy",  by  which  the  Kanawha 
River  was  known  for  many  years.  During  this  period  a 
small  trade  was  established  which  exploited  the  use  of  oil 
for  medicinal  purposes.  It  was  generally  advertised  as  a 
cure-all,  guaranteed  to  alleviate  and  cure  all  the  ills  of 
the  human  body.  Especially  famous  were  the  so-called 
"Seneka  Oils",  and  Krier's  Petroleum  Rock  Oil.  Krier 
was  a  druggist  in  Pittsburgh  who  had  an  excess  production 
of  crude  oil  beyond  that  needed  for  medicinal  purposes.  He 
therefore  erected  a  homemade  still  and  refined  oil,  selling 
the  light  products  for  illuminating  purposes.  During  this 
period  natural  oil  had  to  moot  the  compel  it  ion  of  the  coal- 
oil  industry,  which  was  based  on  the  distillation  of  illumi- 
nating oils  from  coals.  Indeed  the  common  term  "coal-oil", 


POPULAR   OIL  GEOLOGY.  7 

for  kerosene,  is  a  survival  of  this  industry.  In  the  early 
part  of  the  nineteenth  century  it  was  thought  that  the  sup- 
ply of  crude  oil  was  apparently  insufficient  and  was  too 
spasmodic  in  its  occurrence  to  insure  extensive  commercial 
use.  A  few  people,  however,  had  faith  in  the  possibilities 
of  the  natural  oil  and,  in  1854,  organized  the  first  oil 
company  of  America,  "The  Pennsylvania  Kock  Oil  Co." 
Like  many  of  its  successors,  this  company  became  involved 
in  financial  difficulties  and  was  reorganized  in  1858  as  the 
"Seneca  Oil  Co."  This  company  secured  Col.  E.  L.  Drake 
as  superintendent  of  field  operations,  who  drilled  the  first 
well  in  1859,  at  Titusville,  Pennsylvania.  At  a  depth  of 
fifty-eight  feet  a  flow  of  oil  of  twenty-five  barrels  a  day 
was  encountered.  Drake's  well  marks  an  epoch  in  the  his- 
tory of  petroleum  because  it  was  the  first  well  drilled  for 
the  purpose  of  securing  oil.  The  well  demonstrated  the 
feasibility  of  drilling  for  oil.  It  therefore  insured  the 
rapid  development  of  the  petroleum  industry  and  at  the 
same  time  paralyzed  the  coal-oil  industry,  then  at  its 
climax. 

Vigorous  drilling  followed  all  along  the  Allegheny 
River,  spreading  eventually  into  Ohio,  West  Virginia,  In- 
diana, and  New  York,  and  resulting  in  the  development 
of  the  Appalachian  oil  fields,  for  many  years  the  leading 
producer  in  America. 

The  chief  competitor  of  the  Appalachian  field  was  the 
Baku  region  on  the  Caspian  Sea.  Here  the  first  well  was 
drilled  in  1889  and  proved  such  a  heavy  producer  that  the 
news,  which  exceeded  the  most  sanguine  expectations,  was 
regarded  with  suspicion  for  many  years. 

The  development  of  oil  fields  proceeded  slowly  be- 
cause the  progress  everywhere  was  hindered  by  lack  of 
transportation  facilities.  Thus  both  in  the  American  and 
Russian  fields  the  oil  was  hauled  in  carts  to  the  railroad 
stations.  The  first  pipe  line  of  importance  was  laid  in 
1875  from  the  oil  country  to  Pittsburgh.  Russia  quickly 
adopted  this  convenient  method  of  transportation.  As  may 
be  imagined,  the  carters  vigorously  opposed  pipe  lines  and 
went  to  such  extremes  in  attempting  to  prevent  their  con- 


8  POPULAR  OIL  GEOLOGY. 

struction  that  for  several  years  strong  guards  were  main- 
tained. The  construction  of  pipe  lines,  however,  did  not 
solve  the  transportation  problem.  Containers  suitable  for 
water  and  rail  transportation  were  still  lacking.  It  was 
customary  to  ship  the  oil  in  wooden  barrels,  the  cost  of 
which  ordinarily  exceeded  the  value  of  the  oil.  It  re- 
mained for  a  Russian  firm,  Nobel  Brothers,  in  1879,  to 
construct  the  first  tank  steamer.  Thus  the  great  trans- 
portation problems  were  solved;  America  produced  the 
pipe  lines,  Russia  the  tank. 

For  years,  Russia  and  America  were  neck  and  neck 
in  petroleum  production.  Russia,  however,  furnished  most 
of  the  sensations  up  to  1902.  Individual  wells  of  tre- 
mendously large  capacity  were  quite  common.  The  Drooj- 
ba  was  a  gusher,  spouting  oil  three  hundred  feet  high, 
with  a  capacity  of  fifty  thousand  barrels  a  day.  It  was 
uncontrollable  for  four  months.  The  Marko>ff  gusher 
spouted  oil  to  a  height  of  four  hundred  feet,  at  a  rate  of 
about  a  hundred  thousand  barrels  a  day.  Gushers,  such 
as  these  were  responsible  for  the  fact  that  in  1901  Russia 
produced  more  than  one-half  the  world's  output  of  petro- 
leum from  an  area  of  only  ten  square  miles. 

Remarkable  discoveries  in  Texas  and  California  en- 
abled America  to  take  the  lead  in  1903,  since  which  time, 
aided  by  the  tremendous  production  of  the  Oklahoma, 
Kansas  and  California  fields,  this  lead  has  been  gradually 
increasing,  until  today  two-thirds  of  the  world's  produc- 
tion of  petroleum  comes  from  the  United  States. 

Mexico  is  the  third  largest  producer  of  petroleum. 
Its  rapid  development,  so  surprising  because  of  unsettled 
political  conditions,  is  due  to  the  fact  that  Mexico  has 
produced  the  greatest  gushers  known.  Thus  the  famous 
gusher  of  Dos  Bocas,  in  1908,  was  estimated  to  have  a 
capacity  of  two  hundred  and  fifty  thousand  barrels  a  day. 
The  accompanying  tables  show  the  comparative  produc- 
tion of  crude  oil  of  the  various  states  in  the  Union,  as  well 
as  the  production  of  the  more  important  oil  fields  of  the 
world,  as  nearly  as  can  be  ascertained  under  present  con- 
ditions. 


POPULAR  OIL  GEOLOGY. 

World's  Production  of  Crude  Petroleum,  1916. 

United  States  292,300,000  barrels 

Russia    72,360,000  barrels  (1915) 

Mexico    32,910,000  barrels     

Roumania   13,230,000  barrels  (1915) 

Dutch  East  Indies 12,386,000  barrels  (1915) 

Galicia   4,158,000  barrels  (1915) 

India    6,833,000  barrels  (1915) 

Japan   3,431,000  barrels     

Peru,   Etc    2,487,000  barrels     : 


Grand  total   429,119,000  barrels,  1915. 

Production  of  Crude  Oil  in  the  United  States,  1916-1917. 

1916  1917 

Oklahoma    106,000,000  barrels  147,000,000  barrels 

California    91,800,000  barrels  97,000,000  barrels 

Gulf  Coast  23,900,000  barrels  24,900,000  barrels 

Appalachian     20,700,000  barrels  24,600,000  barrels 

Illinois    16,300,000  barrels  15,900,000  barrels 

Kansas    13,000,000  barrels  Included  in  Okla. 

Louisiana   11,800,000  barrels  8,700,000  barrels 

North  Texas    '. .     8,800,000  barrels  

Wyoming    6,700,000  barrels  9,200,000  barrels 

Lima — Indiana    ; .     2,600,000  barrels  3,500,000  barrels 

Crude  Oil  Prices— December,  1919. 
(The  Oil&  Gas  Journal) 

Pennsylvania $4.50      North  Texas $2.50 

Lima  (Ohio) 2.73      Caddo  (La.)   <   2.50 

Illinois 2.77      Canada 3.1-3 

Kansas-Oklahoma   ..    2.50      California 1.23-1.62 

Healdton  (Okla.)   .  .    1.35  Mex.  Crude  .  .  .  .1.05-1.10 

Indiana   . 2.63     Homer  (La.) 2.50 


10 


POPULAR   OIL   GEOLOGY. 


II.    Composition  and  Properties  of 
Oil  ami  Gas 

Elementary  Principles  of  Chemistry. 

Before  discussing  the  composition  of  the  various  kinds 
of  oil  and  gas  found  in  Nature,  it  is  necessary  to  take  up 
very  briefly  a  few  of  the  fundamental  ideas  of  chemistry. 

Elements. 

Chemists  tell  us  that  there  are  about  eighty  elements 
in  Nature.  By  "elements"  they  mean  those  substances  that 
cannot  be  subdivided  by  any  known  process.  Familiar 
examples  are  iron,  copper,  and  sulphur.  It  is  customary 
to  represent  each  element  by  a  symbol;  ordinarily  the 
initial  letter  of  the  word  standing  for  the  element  is  taken. 
Thus,  the  element  carbon,  which  is  the  chief  constituent 
of  coals  and  of  oils,  is  represented  by  the  letter  "C".  The 
other  elements  of  importance  in  this  connection  have  sym- 
bols as  follows: 

Oxygen  O 

Nitrogen  N 

Hydrogen  H 

Sulphur  S 

Compounds. 

Most  of  the  elements  occur  in  Nature  in  combina- 
tions, which  have  characteristic  properties  quite  different 
from  those  of  the  component  elements,  and  which  always 
contain  the  same  proportion  of  each  element  by  weight. 
Such  combinations  are  known  as  "compounds."  For  ex- 
ample, the  mineral  making  up  limestone  is  a  compound 
always  carrying  40%  of  calcium,  12%  of  carbon  and 
48%  of  oxygen. 

11 


12 


POPULAR   OIL  GEOLOGY. 


Table  of  Elements. 
(After    Frazer   and   Brown.) 


Name 

Symbol 

Atomic 
Weight 

State 

Discoverer 

Date 

Aluminum.  .  .  . 

Al 

27.1 

Solid 

Woehler 

1827 

Antimony.  .  .  . 

Sb 

120.2 

•« 

Valentine    .  .  

1460 

Argon  

A 

39  9 

Gas 

I      Rayleigh      ) 

1CQK 

Arsenic  

As 

75.0 

Solid 

{  and    Ramsay  j 
Schroeder 

1694 

Barium  

Ba 

137.37 

Davy 

1808 

Bismuth     .... 

Bi 

208.0 

H 

Agricola    

1529 

Boron  

B 

11.0 

« 

Daw 

1807 

Bromine  

Br 

79.92 

Liquid 

Balard 

1826 

Cadmium  
Caesium  

Cd 

Cs 

112.40 
132.81 

Solid 

Stromeyer    ..... 
Bunsen 

1817 
1860 

Calcium  

Ca 

40  09 

« 

Davy 

1808 

Carbon  

c 

12.00 

«« 

Ancients          .  . 

Cerium. 

Ce 

140  25 

« 

Berz    &  Hisinger 

1803 

Chlorine  

Cl 

35.46 

Gas 

Scheele             * 

1774 

Chromium  

Cr 

52.1 

Solid 

Vauquelin   . 

1797 

Cobalt  

Co 

58  97 

« 

Brandt 

1733 

Columbium.  .  .  . 

Cb 

93.5 

« 

Hatchett   

1803 

Copper  

Cu 

63.57 

« 

Ancients    

Dysprosium.  .  . 

Dy 

162.5 

it 

Erbium  

Er 

167  4 

a 

Mosander 

1843 

Europium 

Eu 

152  0 

u 

Fluorine  

F 

19  0 

Gas 

Moissan         .   ... 

1886 

Gadolinium.  .  .  . 

Gd 

157  3 

Solid 

Gallium  

Ga 

69  9 

de  Boisbaudran 

1875 

Germanium.  .  . 

Ge 

72.5 

.. 

Winkler    

1886 

Glucinum  

Gl 

9  1 

a 

Woehler    

1828 

Gold  

Au 

197  2 

tt 

Ancients 

Helium 

He 

4  0 

Gas 

Ramsay 

1895 

Hydrogen 

H 

1  008 

Caveiidish 

1766 

Indium  

In 

114  8 

Solid 

Reich  &  Richter. 

1863 

Iodine 

I 

126  92 

Courtois    

1812 

Iridium 

Ir 

193  1 

« 

Tennant 

1804 

Iron 

Fe 

55  85 

« 

Ancients 

Krypton  

Kr 

81.8 

Gas 

Ramsay   

1895 

Lanthanum. 

La 

1390 

Solid 

Mosander    

1839 

Lead 

Pb 

207  10 

it 

Ancients    

Lithium 

Li 

700 

« 

Daw 

1818 

Lutecium 

Lu 

174  0 

Solid 

Magnesium 

Me 

24  32 

Daw 

1808 

Manganese 

Mn 

54  93 

Gahn 

1774 

Mercury 

He 

200  0 

Liquid 

A.ncients 

POPULAR   OIL   GEOLOGY. 


13 


Table  of  Elements — Cont. 
(After  Eraser  and  Brown.) 


Name 

Symbol 

Atomic 
Weight 

State 

Discoverer 

Date 

Molybdenum  .  . 

Mo 

96.0 

Solid 

Hjelm    

1782 

Neodymium 

Nd 

144  3 

« 

Neon 

Ne 

20  0 

Gas 

Ramsay 

1895 

Nickel     

Ni 

58  68 

Solid 

Cronstedt   

1751 

Nitrogen     .... 

N 

1401 

Gas 

Rutherford 

1772 

Osmium 

Os 

190  9 

Solid 

Tennant 

1803 

Oxygen  

o 

1600 

Gas 

Priestley       

1774 

Palladium 

Pd 

106  7 

Solid 

Wollaston 

1803 

Phosphorus.  .  . 

p 

31.0 

ii 

Brandt  

1669 

Platinum  

Pt 

1950 

« 

Wood         

1741 

Potassium  

K 

39  10 

« 

Davy 

1807 

Praseodymium 

Pr 

1406 

u 

Radium  

Ra 

2264 

« 

Curie        

1903 

Rhodium  

Rh 

102  9 

M 

Wollaston 

1803 

Rhubidium.  .  .  . 

Rb 

85  45 

U 

Bunsen   

1860 

Ruthenium.  .  .  . 

Ru 

101  7 

11 

Glaus       

1845 

Samarium  
Scandium  

Sa 
Sc 

150.4 
44  1 

« 

de  Boisbaudran.. 
Nilson 

1888 
1879 

Selenium  

Se 

79  2 

„ 

Berzelius 

1817 

Silicon  

Si 

28  3 

« 

Berzelius 

1823 

Silver  

A£ 

107  88 

« 

Ancients 

Sodium  

Na 

23  00 

,< 

Davy 

1807 

Strontium  

Sr 

87  62 

« 

Davy    

1808 

Sulphur  

g 

32  07 

<« 

Ancients 

Tantalum  

Ta 

181  0 

« 

Ekeberg 

1802 

Tellurium  

Te 

127  5 

t( 

Klaproth 

1798 

Terbium  

Tb 

159  2 

tt 

Mosander 

1843 

Thallium  

Tl 

204  0 

„ 

Crookes 

1861 

Thorium  

Th 

232  42 

II 

Berzelius 

1829 

Thulium  

Tm 

168  5 

« 

Cleve 

1879 

Tin  

Sn 

119  0 

I 

Ancients 

Titanium  

Ti 

48  1 

« 

Klaproth 

1794 

Tungsten  

W 

184  0 

( 

De  L/uyart 

1786 

Uranium  

u 

238  5 

« 

Pe'ligot 

1841 

Vanadium  

v 

51  2 

« 

Sefstroem 

1830 

Xenon  

Xe 

128  0 

fr"  Q 

Ramsay 

1895 

Ytterbium  

Yb 

172.0 

Solid 

Marignac  

1872 

(Neoytterbium) 
Yttrium  

Y 

on  A 

Wophlpr    CM 

1040 

Zinc  

Zn 

65  7 

it 

\  Mentioned  by  ) 

1540 

Zirconium  

Zr 

90  6 

K 

|     Paracelsus     ] 
Berzelius 

1824 

14  POPULAR  OIL  GEOLOGY. 

Atoms  and  Molecules. 

The  extremely  minute  particles  of  elements  which 
serve  as  units  of  combination  are  known  as  atoms.  It  has 
been  found  that  all  elements  combine  in  a  definite  propor- 
tion bj  weight.  This  is  known  as  "atomic  weight".  All 
atoms  are  arranged  in  groups,  known  as  molecules.  These 
may  be  conceived  of  as  being  the  smallest  particle  of  any 
substance  that  may  occur  independently  and  still  have  the 
properties  of  that  substance.  It  is  also  customary  to 
express  the  composition  of  compounds  by  symbols.  Thus, 
limestone  is  expressed  by  the  symbol  CaCO3,  which  means 
that  one  molecule,  that  is,  the  smallest  part  of  limestone 
that  can  exist,  is  made  up  of  one  atom  of  calcium,  one  atom 
of  carbon,  and  three  atoms  of  oxygen. 

Both  atoms  and  molecules  are  extremely  small  in  size 
and  probably  will  never  be  visible,  no  matter  how  powerful 
microscopes  may  become.  Thus,  one  cubic  inch  of  nitro- 
gen gas  is  estimated  to  contain  110  billion  billion  atoms. 
It  would  require  76  million  of  these  to  make  a  row  one 
inch  long.  Nevertheless,  there  are  enough  atoms  in  a  sin- 
gle cubic  inch,  if  placed  end  to  end,  to  make  a  row  90 
million  miles  long. 

Natural  Hydrocarbons. 

Oil  and  gas  are  essentially  compounds  of  carbon  and 
hydrogen,  or  to  speak  more  correctly,  mixtures  of  such 
compounds.  There  are  a  great  many  possible  combina- 
tions of  the  two  elements,  carbon  and  hydrogen,  eighteen 
of  which  have  been  found  and  are  known  as  hydrocarbon 
series.  One  of  the  most  important  of  these  carries  carbon 
and  hydrogen  in  the  ratio  of  twice  as  many  plus  two, 
hydrogen  atoms  as  carbon  atoms.  Thus  the  compositions 
may  be  expressed  by  the  symbol  CnH2n+2.  This  series  is 
known  as  the  methane  or  paraffin  series.  As  will  be  evi- 
dent the  molecules  may  carry  a  few  or  very  many  atoms. 
The  less  atoms  in  the  molecule,  the  more  volatile  the  sub- 
stance is.  Thus  CH4  is  a  gas,  known  as  methane,  or  marsh 
gas.  C2oH42  is  a  solid,  known  as  paraffin. 


POPULAR   OIL  GEOLOGY.  15 

Another  series  carries  carbon  and  hydrogen  in  the 
ratio  of  two  hydrogens  to  one  carbon.  Here  also  the  num- 
ber of  atoms  may  vary,  and  we  have  compounds  ranging 
from  C2H4  to  C30H6o-  Two  series  have  this  composition, 
one  known  as  the  olefine  series,  which  is  unstable,  i.  e., 
decomposes  readily.  The  other  series  is  known  as  the 
naphthene  series.  The  paraffin  and  naphthene  series  are 
the  most  important  constituents  of  oil  and  of  gas.  In  addi- 
tion members  of  the  following  series  have  been  found,  but 
all  are  of  very  minor  importance : 

The  acetylene  series CnH2n-2 

The  aromatic  hydrocarbons — 

The  benzene  series.  .  .  . CnH2n— d 
The  naphthalene  series.  .  .CnH2n_i2 
The  anthracene  series.  ..  .CnH2n_i8 

Composition  of  Gas. 

All  gas  occurring  in  Nature  may  be  classified  as  fol- 
lows :  First,  mineral  gas ;  second,  swamp  gas ;  and  third, 
natural  gas.  Mineral  gases  are  of  inorganic  origin.  That 
is,  they  are  not  produced  from  or  by  living  organisms  nor 
from  their  dead  remains.  For  example,  the  gas  escaping 
from  volcanic  craters,  such  as  the  poisonous  hot  gases  which 
rolled  down  Mt.  Pelee  and  destroyed  the  city  of  St.  Vin- 
cent on  Martinique  in  1902,  as  well  as  the  gases  escaping 
from  some  of  the  geysers  of  the  Yellowstone  Park,  are  in- 
organic. 

Swamp  gas  is  formed  at  the  present  time  by  the  decay 
of  vegetable  matter  under  water.  It  is  commonly  found  in 
marshes,  swamps,  and  old  wells.  Swamp  gas  is  essen- 
tially CH4,  which  is  hence  known  by  the  name  "marsh 
gas."  Occasionally  marsh  gas  occurs  in  such  quantities 
that  after  stirring  up  the  bottom  of  the  swamp  vigorously, 
its  surface  may  be  ignited.  The  heat  so  generated  is  fre- 
quently sufficient  to  drive  off  the  water.  In  this  way  shal- 
low swamps  in  the  northern  part  of  Germany  are  fre- 
quently reclaimed  for  agricultural  purposes. 


16  POPULAR   OIL  GEOLOGY. 

Natural  Gas. 

Neither  mineral  gas  nor  swamp  gas  are  of  any  com- 
mercial importance.  All  commercially  valuable  gases 
which  may  be  used  as  fuel  or  a  source  of  light  are  custom- 
arily included  under  the  term  "natural  gas." 

We  distinguish  two  kinds  of  natural  gas,  known  as 
"wet"  gas  and  "dry"  gas.  Dry  gas  is  essentially  CH4,  and 
is  ordinarily  derived  from  decomposing  coal  beds,  very 
rarely  from  oil  pools.  Wet  gas  is  nearly  always  associated 
with  oil  pools.  Some  of  the  heavier  hydrocarbons,  such 
as  gasoline,  frequently  drip  from  this  gas.  Hence  the 
term  "wet".  Since  this  gas  also  has  a  tendency  to  col- 
lect in  the  top  of  well  casings,  it  is  known  as  casing  head 
gas.  Wet  gas  of  this  kind  offers  a  possibility  of  condens- 
ing gasoline  from  it  on  a  commercial  scale.  Plants  of 
this  nature  are  in  active  operation  in  a  number  of  eastern 
states  and  in  California. 

In  composition  natural  gas  is  essentially  CH4.  Wet 
gas  carries  in  addition  C2H4,  and  C2H6.  Gasoline  is  ordi- 
narily present  in  quantities  of  a  few  pints  per  thousand 
cubic  feet.  Occasionally  nitrogen  is  very  high.  Certain 
natural  gases  in  Russia  run  up  to  50%  nitrogen,  while  some 
in  Kansas  exceed  80%.  Practically  every  oil  field  car- 
ries gas.  There  are,  however,  many  gas  fields  in  which 
oil  does  not  occur  in  commercial  quantities.  The  pressure 
on  gas  is  often  enormous  and  so  great  as  to  completely 
wreck  the  drilling  machinery  and  derricks  if  the  gas  is 
struck  unexpectedly.  Pressures  of  from  1,000  to  1,500  Ibs. 
a  square  inch  have  been  recorded  from  New  York.  A 
number  of  wells  located  in  the  Big  Horn  Basin  of  Wyo- 
ming have  an  estimated  capacity  of  more  than  100,000,000 
cubic  feet  a  day. 

The  following  table  gives  the  composition  of  natural 
gas  from  a  few  of  the  prominent  fields  of  the  United 
States : 


POPULAR  OIL  GEOLOGY.  17 

Table  of  Analyses  of  Natural  Gas. 

CH*         C2H0    C2H4     CO2     CO        O          N  H     He     H2S 

Jola,   Kan;    94.00  0  00          0     0.23        5.08  0     0.2 

Dexter,  Kan.   .        .    14.85       0.41         000     0.20  82.70  tr     1.84 


Pittsburgh,    Pa  
Oil  City,  Pa  

98.90 
95.44 

0     0.40 
0.05 

tr 

0.70 
4.51 

.. 

Shimston,   W.  Va.  . 

1509      80.0 

0.4           0 

0.4      0.2 

3.96 

Ohio  — 
Findlay     
Fostoria    . 

92.61 
92.84 

0.3      0.26 
0.20   0.20 

0.50   0.34 
0.55   0.35 

3.96      2.18 
3.82      1.89 

..     0.2 
.     0.15 

Oklahoma  — 

Blackwell    ......    83.40     10.31     0.61       ......        5.19     0.33  0.16 

Indiana  — 
Kokomo     .......         93.6  ..0.4          ..          ..        6.0 

California  — 

Los     Angeles....  83.70        0.2  6.68   0.25  0.25  2.86  6.31 

Greybull,    Wyo  ____  81.70  17.3  ..     0.20  ..  0  0.75 

Byron,     Wyo  ......  64.05  33.28  ..     0.47  ..  0  3.20 

Composition  of  Petroleum. 

The  geologist  includes  all  natural  oils'under  the  term 
petroleum.  Petroleum  is  essentially  a  mixture  of  the 
hydrocarbon  compounds  of  the  CnH2n+2  (paraffin  series), 
and  of  the  series  CnH2n  (define  and  naphthene  series). 
Oils  carrying  essentially  the  first  series  are  known 
as  paraffin  base  oils.  Those  carrying  the  second 
series  are  known  as  asphalt  base  oils.  The  oils  of  Wyo- 
ming and  Pennsylvania  are  paraffin  base  ;  those  of  Texas 
and  California  are  asphalt  base.  Those  of  Illinois  carry 
equal  proportions  of  both  and  therefore  are  known  as  mixed 
base  oils.  Although  oils  are  essentially  compounds  of  car- 
bon and  hydrogen;  sulphur,  nitrogen  and  oxygen  are  also 
present,  as  well  as  other  impurities  of  minor  importance. 
In  percentage  composition,  petroleum  shows  the  following 
extreme  ranges: 

Carbon,  79%  to  88% 


aron,  o 

Hydrogen,  9.6%  to  14.8% 
Nitrogen,  0.02%  to  1.1% 
Sulphur,  Trace  to  4% 


18  POPULAR  OIL   GEOLOGY. 

Sulphur  may  be  present  as  free  sulphur,  or  it  may 
be  present  as  a  sulphide.  In  the  latter  case  it  imparts 
to  the  oil  a  very  disagreeable  odor,  that  of  decomposing 
eggs,  which  is  characteristic  of  the  oils  of  Ohio  and  Texas. 
Nitrogen  is  present  in  the  form  of  complex  organic  com- 
pounds. These  are  frequently  edible,  consequently  such 
oils,  as  for  example  certain  oils  of  California,  when  ex- 
posed to  the  air,  become  quickly  infested  with  maggots. 

Analyses  of  Petroleums. 

C  H  S  N 

Findlay,    Ohio 83.41  13.13  0.56          0.06 

Oil  City,  Pa 85.80  14.04 

Baku,  Russia  86.25  13.48 

Beaumont,  Texas  85.05  12.30  1.75 

Ventura,  Calif 84.00  12.70  0.40          1.70 

McKittrick,    Calif 86.06  11.45  0.87 

Alsace,  Germany    79.50  13.6  6.90  (Oxygen  S  N) 

Rangoon,  Burma  83.80  12.70  3.35 

Java   (DanDang-Ho)    87.10  12.0  0.9 

Burning   Springs,   W.   Va. .   84.3  14.1  1.6 

Amaze,  Japan   84.66  13.22  0.22          0.36 

Specific  Gravity. 

The  weight  of  crude  oils  is  dependent  to  a  consider- 
able extent  on  the  chemical  composition.  Paraffin  base 
oils  are  ordinarily  the  lighter.  Consequently  the  expres- 
sions "light"  oil  and  "heavy"  oil  have  been  used  as  syn- 
onymous with  paraffin  base  and  asphalt  base  oils,  respect- 
ively. The  relative  weight  of  oil  as  compared  with  the 
weight  of  an  equal  volume  of  water  is  known  as  specific 
gravity.  Considering  the1  specific  gravity  of  water  to  be 
one,  oil  lies  between  the  limits  of  0.73  and  1.0.  It  is  more 
customary  to  express  the  weight  of  oil  in  terms  of  degree 
of  the  so-called  Beaume  scale.  This  is  usually  read  direct 
on  a  hydrometer  immersed  in  the  oil.  The  degree  of 
Beaume  goes  up  as  the  weight  goes  down,  therefore  a 
light  paraffin  base  oil  has  a  high  degree  Beaume,  or  is 
said  to  be  a  high  gravity  oil.  A  heavy  asphalt  base  oil 
has  a  low  degree  Beauino,  and  is  said  to  be  a  low  gravity 
oil.  The  appended  table  shows  the  relation  existing  be- 
tween the  degree  Beaume,  the  specific  gravity,  and  the 


POPULAR  OIL  GEOLOGY. 


19 


Sp 


Gallon 


Gr. 


jar 
Barr&l 


5.  323 
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S»2// 


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5T9 
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7825J32A67 
7773 
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767f   322 


7  620  3 20.  06  57ooS 


35 


4-9 
5~0 
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Figure  4.    Table  showing  the  relation  existing  between  specific 
gravity  and  weight  of  oil. 

(Payne  &   Stroud) 


20 


POPULAR   OIL   GEOLOGY. 


POUNDS    ffft    CUBIC    FOOT 


POPULAR  OIL  GEOLOGY.  21 

weight  of  crude  oil.     The  second  table  shows  the  specific 
gravity  of  a  few  typical  oils. 

Specific  Gravity  of  Typical  Oils. 

Sp.  Gr.  Be\ 

Pennsylvania    0.801   —0.817  46.2  —  42.6 

Ohio    0.816    —0.860  42.8  —  32.5 

Kansas    0.835    —1.000  38.8  —  10.0 

Colorado — 

Boulder    0.814  42.0 

Debeque    0.809  43.0 

Shale  Oil   0.9138  23.0 

West  Virginia  0.841    —  0.873  37.6  —  30.0 

California    0.920    —0.873  30.0  —  12.3 

Dutch  East  Indies 0.765    —0.791  53.0  —  47.0 

Peru    0.815—0.945  38.0 

Roumania    0.736    —0.8894  27.0  —  60.0 

Mexico    0.809    —1.000  43.0  —  10.0 

Wyoming — 

Greybull    0.786  48.2 

Grass  Creek  0.8187  41.0 

Grass  Creek  0.7984  45.3 

Byron    0.8174  42.0 

Cody    0.8454  35.6 

Salt  Creek 0.8221  40.3 

Salt  Creek    0.8255  39.6 

Shannon    0.910        .  24.0 

Lander    0.9198  22.2 

Lander    0.9126  23.4 

Lander    0.9091  24.0 

Plunkett    0.8121  42.4 

Pilot  Butte  0.875  30.0 

Distillation  Tests. 

The  percentage  of  the  various  products  yielded  on 
refining  is  most  frequently  used  as  a  basis  for  comparing 
the  different  oils.  Refining  is  simply  a  distillation  pro- 
cess in  which  the  oil  is  heated  in  retorts  at  various  tem- 
peratures and  the  volatile  material  driven  off  and  con- 
densed. The  very  volatile  matter  is  given  off  at  low  tem- 
peratures, the  less  volatile  at  increasingly  higher  tempera- 
ture. The  final  residue  is  known  as  the  base.  This  may 
be  commercially  valuable  paraffin,  as  in  the  case  of  light 
oils,  or  an  oxidized  residue,  which  we  call  asphalt.  A 
distillation  analysis  shows  ordinarily  four  or  five  products. 


22 


POPULAR  OIL   GEOLOGY. 


First,  the  volatile  oils,  which  include  gasoline,  naphtha, 
and  benzene;  second,  the  illuminating  oils,  or  kerosene; 
third,  the  lubricating  oils ;  fourth,  fuel  oils,  which  are  of 
chief  importance  in  the  asphalt  base  oils ;  and  last,  paraf- 
fin, if  present  in  commercial  quantities.  The  following- 
table  gives  the  result  of  distillation  tests  on  a  few  typical 
American  oils: 


1 

Volatile  Oils   12.0 

Illuminating   Oils 67.0 

Lubricating  Oils 12.5 

Fuel   Oils    4.0 

Paraffins    .   2.0 

1.  Appalachian 

2.  Lima,  Ohio 

3.  Illinois 


2 

3 

4 

5 

6 

11.5 

3.5 

11.0 

3.0 

6.0 

43.0 

39.0 

41.0 

15.0 

18.0 

15.0 

6.0 

1.5 

25.0 

56.0 

45.0 

73.0 

72.0 

2.0 

4.  Oklahoma 

5.  Texas — Louisiana 

6.  California 


Distillation  Tests  of  Wyoming  and  Colorado  Oils. 


Locality — 


Volatile 
Oils 


Greybull,  Wyo 31.0 

Basin,    Wyo 

Basin,    Wyo 26.0 

Basin,    Wyo 30.5 

Grass  Creek,  Wyo.  22.0 
Grass  Creek,  Wyo.  35.0 

Cody,  Wyo 

Cody,  Wyo ... 

Byron,  Wyo 29.0 

Salt  Creek,  Wyo. .     8.0 
Salt  Creek,  Wyo..   11.0 

Shannon,  Wyo 

Shannon,  Wyo 

Lander,    Wyo 2.5 

Lander,    Wyo 2.0 

Plunkett,  Wyo 14.0 

Pilot  Butte,  Wyo..   19.0 

Douglas,  Wyo 8.0 

Douglas,   Wyo 

Rangeley,  Colo 

Rangeley,   Colo 25.0 

De  Beque,  Colo. . .     1.0 

De  Beque,  Colo 

Boulder,  Colo 20—22 

Florence,   Colo. . .     4.15 


Illumi- 
nating 

Oils 

32.5 

22.5 

34.5 

38.0 

42.0 

32.0 

37.0 

48.0 

42.5 

38.0 

34.0 

12.5 

10.0 

22.0 

23.5 

41.0 

59.0 

38.5 
6.0 

60.0 

45.0 

42.0 

27.0 
38—40 
30.45 


Residue 
36.5 
77.5 
39.5 
31.5 
36.0 
33.0 
59.6 
52.4 
28.5 
49.3 
54.0 
86.9 
86.6 

6*9.9 
41.1 
22.0 
53.5 


27.0 
56.5 
70.9 
40.0 
65.4 


Gravity 

Paraffin 

Be 

48.2 

.  .  . 

27.5 

39.5 

45.6 

41.0 

.  .  . 

45.3 

35.6 

. 

38.0 

.  .  . 

41.0 

4.97 

40.3 

5.56 

38.4 

1.14 

23.9 

.  .  . 

24.1 

22.2 

0.91 

23.4 

42.4 

.  .  . 

30.0 

2.00 

35.9 

.  . 

20.4 

20.00 

43.6 

37.8 

.  . 

25.6 

POPULAR  OIL  GEOLOGY.  23 

Miscellaneous  Properties. 

The  color  of  oils  is  variable  and  depends  mainly  on 
composition.  Paraffin  base  oils  are  the  lighter;  yellow  to 
brown  by  transmitted  light,  green  by  reflected  light. 
Asphalt  base  oils  are  ordinarily  dark  brown  to  deep  black 
in  color. 

The  odor  of  certain  oils  is  quite  characteristic.  The 
oils  of  Pennsylvania  and  Wyoming  have  the  odor  of  gaso- 
line. California  oils  have  a  pleasant  aromatic  odor.  The 
oil  of  the  East  Indies  has  the  odor  of  oil  of  cedar.  Ohio, 
Indiana,  Ontario,  and  much  of  the  Texas  oil  has  the 
unpleasant  odor  of  hydrogen  sulphide. 

Another  property  of  importance  is  viscosity,  which 
may  be  defined  as  the  internal  resistance  offered  to  flow. 
Paraffin  base  oils  are  ordinarily  quite  fluid.  Asphalt  base 
oils  are  viscous.  Viscosity  has  quite  an  important  effect 
on  the  transportation  of  oils.  Some  oils  flow  with  such 
reluctance  that  they  must, be  heated  before  they  can  be 
pumped  through  a  pipe-line.  Oils  that  remain  fluid  at 
temperatures  of  about  0°,  are  known  as  winter  oils.  Those 
which  remain  fluid  only  at  temperatures  of  40  degrees  or 
higher,  are  summer  oils.  Summer  oils  are  the  heaviest 
oils,  with  high  viscosity,  which  can  only  be  shipped  during 
the  summer  season. 

Other  physical  properties,  such  as  surface  tension, 
optical  activity,  refraction,  and  expansion  upon  heating 
are  frequently  determined.  They,  however,  possess  only 
a  slight  practical  value  and  are  more  important  from  the 
theoretical  standpoint;  hence  they  will  not  be  discussed 
in  detail. 

Solid  and  Semi-Solid  Hydrocarbons. 

There  are  other  natural  hydrocarbons  besides  gas  and 
oil.  As  a  matter  of  fact,  all  gradations,  both  chemical 
and  physical  may  be  found  from  natural  gas  through  oil 
into  viscous  and  even  solid  bodies.  A  few  of  these  deserve 
special  mention.  A  viscous  pasty  black-colored  hydro- 
carbon, representing  the  residue  from  evaporating  heavy 


24  POPULAR  OIL  GEOLOGY. 

^ 

oil,  is  known  as  "maltha"  or  "chapopote".  The  natural 
wax  or  paraffin,  ordinarily  the  result  of  evaporation  of 
high-grade  oil,  is  known  as  "ozokerite".  "Gilsonite"  and 
"grahamite"  are  very  valuable,  brilliant,  black-colored, 
solid  and  brittle  hydrocarbons,  useful  chiefly  for  varnishes, 
shellacs,  and  enamels.  "Lake  asphalt"  is  known  only 
from  the  Island  of  Trinidad,  and  is  a  highly  viscous,  semi- 
solid  substance,  similar  to  common  asphalt. 

Occasionally  the  pores  and  openings  in  rocks  are  com- 
pletely saturated  with  residues  left  by  the  evaporation  of 
oils.  Such  rocks  are  known  as  "bituminous  rocks".  Sand- 
stones, shales,  and  limestones,  as  well  as  gravels  of  this  sort 
are  known  and  are  used  quite  extensively  for  road  metal. 


III.  Tne  Origin  of  Oil  and  Gas 

Two  questions  are  involved  in  any  discussion  of 
the  origin  of  natural  hydrocarbons.  The  first  one  con- 
cerns the  original  materials  from  which  oil  and  gas  are 
derived;  the  second  deals  with  the  manner  and  methods 
by  which  this  material  ultimately  changes  into  oil  and 
gas.  The  first  question  is  fundamentally  a  geological 
one ;  the  second  is  essentially  a  chemical  and  physical  one. 

Classification  of  Theories  of  Oil  Origin. 

The  nature  of  the  original  materials  from  which  the 
hydrocarbons  are  formed  is  a  much  disputed  question.  In 
general,  all  theories  of  origin  fall  in  one  of  two  classes, 
which  for  convenience  we  may  call  "inorganic  theories", 
and  "organic  theories".  Those  of  the  first  class  maintain 
that  the  hydrocarbons  are  derived  from  inorganic  materi- 
als. The  second  class,  on  the  other  hand,  maintains  their 
derivation  from  the  remains  of  plants  and  animals. 

Inorganic  Theories. 

The  older  and  more  strictly  chemical  theories  postu- 
late a  derivation  from  inorganic  substances.  Some  of 
these  theories  are  very  crude  and  purely  speculative. 
Others  are  more  refined,  and  are  based  on  exhaustive  lab- 
oratory work  and  synthetic  experiments  carried  on  by  Rus- 
sian and  French  chemists.  Although  there  are  a  number 
of  inorganic  theories,  attention  will  only  be  called  to  two 
representative  ones. 

Cosmic  Theory. 

One  of  the  older  ideas  was  that  both  oil  and  gas  were 
constituents  of  the  original  nebular  matter  from  which 
our  solar  system  was  formed;  that,  as  the  earth  cooled 
down  from  high  temperatures,  the  oil  was  precipitated  as 
rain,  was  disseminated  through  the  rocks,  and  was  subse- 
quently collected  in  reservoirs  to  give  us  our  oil  fields. 
This  theory,  also  known  as  the  "Cosmic  Theory",  is  an 

25 


26 


POPULAR   OIL   GEOLOGY. 


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POPULAR  OIL  GEOLOGY.  27 

example  of  the  purely  speculative  type,  which  has  abso- 
lutely no  scientific  foundation  behind  it. 

Mendeleef  s  Carbide  Theory. 

As  an  example  of  the  more  refined  chemical  theories 
we  may  mention  the  theory  of  Mendeleef,  who  presup- 
poses the  existence  of  metallic  carbides  in  the  interior  of 
the  earth.  (Metallic  carbides  are  compounds  of  a  metal 
and  carbon,  similar  to  the  calcium  carbide  which  is  used 
extensively  for  the  generation  of  acetylene  gas.)  These 
carbides,  at  high  temperatures  in  the  interior  of  the  earth, 
react  with  water  to  form  acetylene,  just  as  this  gas  is  pro- 
duced in  our  commercial  carbide  plants.  Subsequently, 
when  subjected  to  different  degrees  of  heat  and  pressure 
this  acetylene  is  changed  into  the  various  hydrocarbons 
found  in  Nature. 

Inorganic  theories  are  more  generally  accepted  among 
chemists  than  among  geologists.  Eugene  Coste,  a  Cana- 
dian geologist,  however,  is  the  most  vigorous  advocate  of 
this  view,  and  cites  the  following  facts  among  others, 
which  he  believes  definitely  proves  that  oil  is  derived  from 
inorganic  materials: 

1.  Hydrocarbons  have  been  found  in  meteorites. 

2.  Hydrocarbons  have  been  fourtd  in  the  spectra  of 
the  stars  and  nebulae. 

3.  Hydrocarbons  have  been  made  artificially  in  the 
laboratory  from   inorganic  materials. 

4.  They  have  been  found  in  igneows  rocks,  in  veins, 
and  in  volcanic  emanations. 

5.  Minute  quantities  have  been  found  in  cast  iron. 
It  may  be  of  interest  to  add  in  this  connection  that 

there  is  a  strong  probability  that  the  oil  that  occurs  in 
igneous  rocks  and  in  volcanic  emanations  is  derived  from 
some  oil-bearing  rocks  under  the  earth's  surface,  and  con- 
sequently not  inorganic.  In  any  attempt  to  discover  the, 
origin  of  petroleum,  we  must  carry  in  mind  the  fact  that 
the  question  at  issue  is  not  "How  may  petroleum  be  pro- 
duced", but  "How  can  commercial  accumulations  of  oil 
be  formed  ?"  Although  all  geologists  are  willing  to  admit 


28  POPULAR  OIL  GEOLOGY. 

the  possibility  of  oil  formation  from  inorganic  materials, 
by  far  the  greater  majority  deny  the  probability  of  pro- 
ducing large  quantities  in  this  way.  There  is  absolutely 
no  evidence  to  show  that  the  oil  of  any  commercial  field  is 
derived  from  inorganic  sources. 

Organic  Theories. 

There  are  a  number  of  different  theories  which  post- 
ulate the  derivation  of  hydrocarbons  from  the  dead  re- 
mains of  organisms.  Five  such  groups  of  theories  are 
worth  specific  mention,  all  of  which  differ  in  that  they 
start  with  different  organic  materials.  These  postulate 
one  of  the  following  as  original  materials : 

1.  Coal  and  similar  carbonaceous  matter. 

2.  Accumulation  of  plant  remains. 

3.  Accumulation  of  animal  remains. 

4.  Oozes,  muds,  and  slimes  made  up  in  large  part 

of  the  remains  of  micro-organisms. 

5.  Plant  and  animal  remains  in  combination. 
Within  the  limits  of  this  discussion,  it  is  impossible 

to  treat  all  of  these  in  detail.  Several  of  these  theories 
may  be  selected  as  most  representative,  and  will  be  briefly 
described : 

Coal  Theory. 

The  oldest  of  the  organic  theories  postulates  a  deri- 
vation of  oil  from  coal  fields,  and  is  suggested  by  the  associa- 
tion of  coal  and  oil  in  the  older  known  fields.  It  is  also 
a  fact  worth  noting  that  certain  of  the  gases  which  escape 
from  coal  and  which  are  often  so  dangerous  in  mines  are 
similar  in  composition  to  the  hydrocarbons;  in  oil  fields. 
Again,  it  is  possible  to  distill  from  coal,  at  nigh  tempera- 
ture and  pressure,  certain  gases  and  oils,  indistinguishable 
from  those  met  in  Nature.  In  this  connection  attention 
has  already  been  called  to  the  derivation  of  the  word  "coal 
oil",  which  is  used  synonymously  with  kerosene,  and  which 
emphasizes  the  fact  that  illuminating  oils  were  originally 
manufactured  from  coal.  In  scvcrnl  localities,  as  for  ex- 
ample, in  Scotland,  at  \Vmlcc  in  France,  and  on  the 


POPULAR  OIL  GEOLOGY.  29 

Island  of  Trinidad,  oils  may  be  seen  oozing  out  of  coal 
beds.  In  recent  years,  however,  a  great  number  of  oil 
fields  have  been  found  which  show  no  relation  whatever  to 
coal  fields,  and  which  consequently  throw  discredit  on  the 
idea  that  all  oils  are  derived  from  coal.  In  a  few  cases 
the  theory  is  capable  of  application,  and  at  least  tentatively 
established. 

Plant  Theory. 

There  are  many  modifications  of  the  theory  which 
postulates  a  derivation  from  plants.  Probably  the  one 
best  established  states  that  gelatinous  plants,  such  as  algae, 
are  most  likely  to  give  oil  under  favorable  conditions.  In- 
deed, all  our  knowledge  of  the  chemical  principles  in- 
volved lead  us  to  the  belief  that  plants  with  hard,  woody 
tissue  are  more  likely  to  yield  coal  rather  than  oil.  The 
adherents  of  this  theory  believe  that  the  accumulated  re- 
mains of  gelatinous  plants  forming  along  the  ocean  shore, 
are  buried  under  the  mud  and  sand,  accumulating  there, 
and  are  protected  in  this  way  from  decomposition.  Sub- 
sequently those  remains  are  distilled  into  the  various 
gases  and  oils  met  in  Nature.  In  the  laboratory,  it  is  pos- 
sible to  distill  oils  from  such  plant  remains.  Geographic 
study  proves  that  such  plants  accumulate  in  considerable 
abundance.  Therefore  the  probability  of  such  origin  must 
be  granted.  As  a  matter  of  fact,  certain  of  our  oils  very 
high  in  paraffin,  such  as  the  oils  of  Pennsylvania,  are 
probably  of  this  derivation. 

Engler-Hoefer  or  Dual  Theory. 

The  strict  vegetable  origin  cannot  explain  all  oils. 
Thus  the  many  oils,  high  in  nitrogen,  sulphur,  and  with 
an  asphalt  base,  can  probably  not  be  derived  from  plants 
alone.  On  the  other  hand,  there  are  many  objections  to 
the  theories  which  attempt  to  explain  the  derivation  of 
oil  and  gas  from  animal  remains  alone.  Thus,  for  exam- 
ple, it  is  necessary  to  dispose  of  virtually  the  entire  nitro- 
gen content  and  preserve  at  the  same  time  the  fat  of  the 
animal.  The  abundance  of  scavengers  in  the  ocean  which 


30 


POPULAR   OIL   GEOLOGY. 


POPULAR  OIL  GEOLOGY.  31 

will,  under  ordinary  conditions,  devour  the  dead  bodies  of 
all  animals,  is  often  cited  as  another  objection  against  this 
theory.  Because  of  these  reasons  the  so-called  "Dual- 
theory"  has  been  developed  which  postulates  a  derivation 
of  oil  and  gas  from  both  plant  and  animal  remains.  Prob- 
ably the  greater  number  of  geologists  favor  this  view,  at 
the  same  time  emphasizing  the  relatively  greater  import- 
ance of  animal  remains  as  a  source  of  oil.  It  is  believed 
that  the  decay  of  dead  plants  and  animals  is  retarded  by 
the  salinity,  or  perhaps  coldness,  of  the  ocean  water  at 
the  time  of  accumulation,  and  that  there  is  a  sort  of  select- 
ive putrefaction  followed  subsequently  by  burial.  As  a 
result  of  later  distillation  our  oils  are  formed.  In  this 
connection  it  is  of  interest  to  note  that  a  number  of  differ- 
ent chemists  have  succeeded  in  making  oils  from  mixtures 
of  plant  and  animal  remains  in  the  laboratory,  which  were 
in  every  respect  similar  to  natural  oils. 

That  the  animal  theories  are  fully  competent  to  meet 
all  the  requirements  of  commercial  oil  fields  is  certain,  in 
spite  of  the  greater  liability  of  the  rapid  decomposition 
and  of  being  eaten  by  scavengers.  Thus  it  has  been  esti- 
mated that  the  annual  catch  of  herring  in  the  North  Sea 
for  1300  years  is  sufficient  to  yield  all  the  oil  produced  in 
Galicia.  If  we  carry  in  mind  the  fact  that  the  annual 
catch  of  herring  is  only  an  insignificant  fraction  of  the 
total  number  of  herring  in  the  North  Sea,  and  that  the 
herring  themselves  represent  an  infinitesimally  small  por- 
tion of  animal  life  in  the  oceans,  the  fact  becomes  appar- 
ent that  the  most  insignificant  fraction  of  life  forms  only 
need  be  preserved  to  give  us  all  the  oil  we  find  in  Nature. 
It  is  certain  that  the  organic  origin  of  oil  is  best  supported 
both  by  the  geological  evidence  and  by  the  chemistry  of  the 
hydrocarbons.  Animals  are  probably  the  most  important 
source.  There  is  no  evidence  to  show  that  any  commercial 
oil  field  derives  its  oil  from  inorganic  materials. 

Processes  of  Oil  Formation. 

In  the  preceding  discussion  we  have  come  to  the  con- 
clusion that  organic  matter  represents  the  raw  materials 


OZ  POPULAR  OIL  GEOLOGY. 

from  which  petroleum  is  produced.  We  shall  now  discuss 
the  manner  and  methods  by  which  these  have  become  con- 
verted into  the  different  kinds  of  oils.  A  great  deal  of 
experimental  work  in  the  synthesis  of  oil  has  been  done 
by  chemists,  much  of  it,  however,  under  conditions  not 
found  in  Nature.  As  a  result  a  number  of  false  ideas  have 
been  advanced  and  have  gained  current  acceptance.  Rea- 
soning and  work  along  this  line  should  be  based  on  condi- 
tions as  determined  by  geological  observation.  Thus  we 
know: 

1.  That  the  formation   of  petroleum   is   a  general 
process. 

2.  That  the  original  materials  represent  both  animals 
and  plants. 

3.  That  the  process  of  alteration  is  one  of  selective 
putrefaction  and  distillation,  taking  place  under  the  fol- 
lowing conditions : 

a.  At  comparatively  low  temperatures. 

b.  Under  comparatively  great  pressures. 

c.  In  the  presence  of  water,  usually  salty. 

d.  During  a  great  space  of  time. 

The  temperature  under  which  the  alteration  takes 
place  can  be  determined  roughly  by  the  depth  of  burial  of 
the  oil  rock.  There  is  every  reason  to  believe  that  this 
probably  never  exceeds  300  degrees  Centigrade.  The  pres- 
sure is  at  least  partially  due  to  the  weight  of  the  over-lying 
rocks,  and  in  most  cases  is  probably  not  less  than  one  ton 
a  square  inch. 

Causes  of  Varieties  of  Oil. 

In  the  preceding  discussion  we  have  called  attention 
to  the  fact  that  there  are  different  kinds  of  oils  in  Nature, 
such,  for  example,  as  paraffin  base  oils,  asphalt  base  oils, 
oils  high  in  sulphur,  or  high  in  nitrogen.  A  number  of 
explanations  have  been  advanced  to  account  for  these  varie- 
ties. These  may  be  tabulated  as  follows: 


POPULAR  OIL  GEOLOGY.  33 

1.  Difference  in  the  original  organic  material. 

2.  Physical  conditions  at  the  time  of  formation. 

3.  Migration  and  resulting  filtration  of  oil. 

4.  The  age  of  the  oil. 

A  number  of  American  geologists  believe  that  the 
character  of  oil  depends  upon  the  nature  of  the  original 
organic  material.  They  believe  that  high-grade  paraffin 
oils  are  derived  from  gelatinous  plants;  that  asphalt  base 
oils  are  derived  from  animal  remains;  that  the  high  per- 
centage of  nitrogen  and  sulphur  present  in  certain  oils 
indicates  also  animal  origin.  A  larger  number  dissent 
from  this  view  and  believe  that  physical  conditions  or  the 
age  of  the  oil  will  determine  its  character,  and  that  the 
same  type  of  organic  material  may  give  all  the  varieties 
of  oil  we  have,  depending  upon  physical  conditions  at  the 
time  of  formation.  Thus  there  is  much  evidence  to  show 
that  high  pressure  means  the  retention  of  volatile  con- 
stituents and  a  light  oil.  High  temperature  means  a  rapid 
formation  of  oil  and  a  production  of  much  asphalt.  Low 
heat  means  a  slow  gradual  change  with  the  production  of 
paraffin. 

There  is  good  reason  for  the  belief  that  oil  is  seldom 
retained  in  the  place  where  formed.  Ordinarily  it  has 
migrated  through  the  rocks  and  become  entrapped  subse- 
quently in  a  reservoir.  In  moving  through  the  earth's 
crust,  oils  seep  through  various  kinds  of  rocks,  all  of  which 
may  exert  some  influence.  Thus  oils  traveling  through 
clays  are  separated  into  two  portions,  a  light  oil,  which 
percolates  through  the  clay,  and  a  heavy  residue  which  is 
retained.  That  this  process  is  active  in  Nature  is  certain. 

Another  explanation  is  based  on  the  fact  that  there 
are  a  definite  series  of  stages  in  the  alteration  of  organic 
matter  to  oil ;  that  the  older  oil  is  the  better,  and  that  the 
older  oil  retains  the  greater  proportion  of  gas.  The  fol- 
lowing table  shows  in  graphical  manner  the  stages  in  the 
alteration  of  fats  and  waxes  into  oil. 


POPULAR   OIL  GEOLOGY. 

Animal  and  Vegetable  Residue. 
(Fats  and  Waxes) 


Liquid  Paraffins 
and  gases 


Olefines 
(CH  J 


Solid  Paraffins 


Liquid          Olefines     Naphthenes 
Paraffins        (C  H    )         (C  H    ) 


<   TT 

nH 


Polyolefines 


Liquid  Paraffins 
and  gases 


Naphthenes 


Lubricating  Oils 


Liquid  Paraffins 
and  gases 


Lubricating  Oils 
(Low  in  Hydrogen) 


Naphthenes 


The  table  shows  that  the  first  products  of  distillation 
of  fats  and  waxes  are  stable  paraffins  and  defines,  and 
unstable  solid  paraffins.  The  solid  paraffins  produced, 
break  up  into  liquid  paraffins  and  naphthenes,  both  of  which 
are  stable  and  remain  unaltered,  while  the  olefines  pro- 
duced from  the  original  fats  and  waxes  as  well  as  from 
the  solid  paraffins,  break  up  into  poly-olefines,  which  in 
turn  are  distilled  to  form  liquid  paraffins,  naphthenes,  and 
lubricating  oils.  As  in  the  case  of  the  first  distillation, 
the  liquid  paraffins  and  naphthenes  remain  unaltered,  but 
the  lubricating  oils  break  up  to  form  more  of  the  light  par- 
affins and  naphthenes,  and  in  addition  relatively  stable 
lubricating  oil,  low  in  hydrogen. 

To  summarize,  we  may  conclude  that  the  varieties  of 
oils  may  be  caused  in  part  by  differences  in  the  material 


POPULAR   OIL  GEOLOGY.  35 

from  which  they  are  formed,  and  in  greater  part  they  may 
represent  the  result  of  alteration  of  the  same  material  un- 
der different  conditions.  High  temperature  and  conse- 
quently rapid  alteration  mean  a  heavy  asphalt  base  oil, 
chiefly  useful  as  fuel.  Low  temperature,  high  pressures, 
slow  alteration,  old  age,  and  much  migration  result  in  high- 
grade  light  oil,  extremely  valuable  because  of  the  high 
proportion  of  gasoline  and  other  volatile  constituents  re- 
tained. 


IV.   Rocks  and  Tkeir  Properties 

Classification  of  Rocks. 

Geology  as  applied  to  petroleum  work  is  concerned 
with  the  different  kinds  of  rocks  and  with  their  arrange- 
ment in  the  earth's  surface.  It  is  customary  to  divide  all 
rocks  into  three  great  classes,  known  as  "igneous  rocks' ', 
"sedimentary  rocks",  and  "metamorphic  rocks",  respec- 
tively. 

The  igneous  rocks  represent  those  that  have  solidified 
from  an  originally  -molten  condition.  They  may  reach  the 
earth's  surface  like  the  lavas  flowing  from  volcanoes,  or 
they  may  harden  deep  below  like  granite.  The  sedimentary 
rocks  represent  materials  deposited  in  layers  by  the  action 
of  the  waves,  of  the  wind,  or  of  ice.  In  small  part  they 
also  represent  materials  deposited  from  solution.  They 
accumulate  most  commonly  under  water  in  oceans,  seas, 
lakes  and  rivers.  The  metamorphic  rocks  were  originally 
igneous  or  sedimentary  rocks  that  have  been  so  acted  upon 
by  heat  or  pressure  subsequent  to  their  formation,  that 
they  have  lost  their  original  characteristics.  Both  meta- 
morphic and  igneous  rocks  are  frequently  included  under 
the  term  "crystalline".  In  physical  characteristics  they 
are  quite  compact  rocks,  ordinarily  very  hard,  and  crystal- 
line in  structure.  They  never  carry  commercial  accumu- 
lations of  oil. 

Kinds  of  Sedimentary  Rocks. 

We  recognize  four  kinds  of  sedimentary  rocks;  con- 
glomerates, sandstones;  shales  and  limestones.  Conglom- 
erates are  gravels  consolidated  into  rock;  Sandstones,  as 
the  name  implies,  represent  consolidated  sands ;  Shales  are 
hardened  and  consolidated  muds  and  clays;  while  Lime- 
stone represents  the  accumulations  of  the  hard  parts  and 
shells  of  various  marine  animals,  such  as,  corals,  oysters, 
and  other  shell  fish. 

36 


POPULAR   OIL  GEOLOGY.  37 

Conglomerate. 

Conglomerate  ordinarily  represents  the  coarse  mate- 
rial deposited  along  the  edge  of  the  ocean  shore.  It  con- 
sists of  boulders  of  various  sizes  cemented  to  a  greater  or 
lesser  degree.  The  boulders  and  pebbles  are  usually  well 
worn  and  rounded.  Rocks  made  up  of  angular  fragments 
instead  of  boulders  are  known  as  breccias.  Conglomerates 
are  of  minor  importance  in  oil  fields. 

Sandstones. 

The  sandstones  are  chiefly  made  up  of  grains  of  the 
mineral  quartz.  A  cement  of  oxide  of  iron  gives  the  rock  a 
color  varying  from  pale  yellow  to  a  deep  red  or  brown. 
Lirne,  or  calcium  carbonate  and  silica  form  the  common 
cement  of  the  white  sandstone. 
Shales. 

Shales  are  very  compact  rocks  made  up  of  excess- 
ively fine-grained  material,  especially  mud  and  clay. 
The  shales,  to  a  greater  degree  than  sandstones  and  con- 
glomerates, show  a  well-defined  bedding.  Their  most  char- 
acteristic property  is  to  split  in  thin,  paper-like  sheets. 
Oil-bearing  shales  are  dull  in  color.  Black,  dark  gray,  or 
dull  brown  are  the  most  common.  Bright-colored  shales, 
such  as  red  or  green  of  various  shades,  are  the  exception 
in  oil  regions. 

Limestones. 

Limestones  are  essentially  calcium  carbonate.  They 
may  have  various  colors,  but  dull  drab  colors  are  the  most 
characteristic  in  oil  fields.  Limestones  tend  to  occur  in 
beds  thicker  and  considerably  harder  than  the  layers  of 
shale.  They  can  be  recognized  by  the  fact  that  a  fragment 
dropped  in  a  glass  containing  a  strong  mineral  acid  will 
effervesce  vigorously.  Occasionally  it  may  be  necessary 
to  heat  the  acid  in  order  to  get  the  effervescence, 
Transitional  Rocks. 

The  sedimentary  rocks  do  not  commonly  occur  in  pure 
layers.  Thus,  sandstones  are  very  frequently  mixed  with 
a  small  amount  of  clay,  while  shales  frequently  contain  a 


38  POPULAR  OIL  GEOLOGY. 

small  amount  of  disseminated  sand.  The  same  is  true  of 
limestone.  For  these  reasons  we  speak  of  shaly  sand- 
stone, calcareous  sandstones,  shaly  limestones,  sandy  shales, 
and  calcareous  shales.  All  of  these  terms  are  self-explana- 
tory in  meaning.  The  relationship  is  shown  graphically 
on  the  accompanying  triangular  diagram. 

Sandstone 

/  \ 

Calcareous  Sandstone      Shaly  Sandstone 

/  \ 

Sandy  Limestone  Sandy  Shale 

/       -  \ 

Limestone — Shaly  Limestone — Calcareous  Shale — Shale 

Formation. 

Sedimentary  rocks  may  consist  of  a  collection  of 
pure  sandstones,  pure  shales,  or  pure  limestones,  but  more 
frequently  they  consist  of  several  of  these  rocks  in  more 
or  less  rapidly  alternating  layers.  Any  collection  of  such 
strata  which  may  be  conveniently  considered  together  is 
known  as  a  "formation".  In  order  to  distinguish  forma- 
tions, it  is  customary  to  apply  the  name  of  a  town,  river, 
mountain  or  other  geographic  locality  to  it.  Thus  we  have 
a  Denver  formation,  a  Big  Horn  formation,  a  Niagara  for- 
mation, and  many  others. 
Stratification. 

The  sedimentary  rocks  occur  in  more  or  less  well- 
defined  and  parallel  layers  or  beds.  These  were  originally 
horizontal.  Each  individual  layer  is  spoken  of  as  a 
stratum,  and  the  sedimentary  rocks  are  said  to  be  strati- 
fied. Strata  may  be  massive  layers  as  much  as  ttventy 
feet  in  thickness,  or  they  may  be  thin  and  platy  like  sheets 
of  paper.  In  the  latter  case  the  rocks  are  said  to  be  lami- 
nated. 
Cross  Bedding. 

Occasionally  the  well-defined,  massive  beds  of  rocks 
are  made  up  of  many  smaller  inclined  layers.  The  incli- 
nation of  these  may  be  more  or  less  constant,  which  is  true 
of  those  sediments  that  are  deposited  by  strong  currents  of 
water.  In  other  rocks  these  inclined  layers  may  be  very 


POPULAR   OIL   GEOLOGY.  39 

eccentric  and  irregular  in  direction,  suggesting  the  deposi- 
tion by  the  shifting  winds.  Any  inclined  lamination  of 
this  sort  is  known  as  cross-bedding.  It  is  most  character- 
istic of  sandstones. 

Variations  in  Rocks. 

All  rocks  show  more  or  less  tendency  to  vary  in  their 
characteristics.  This  is  especially  true  of  their  thickness. 
Changes  in  composition  are  also  common.  One  rock  may 
grade  into  another  when  traced  over  a  large  area.  The 
pure  limestone  layers  deposited  in  the  quiet  and  deeper 
parts  of  the  oceans  today,  change  into  shaly  limestones  and 
eventually  into  shale  as  we  approach  the  ocean  shore. 

Erosion  Forms. 

The  configuration  of  the  earth's  surface  is  subject  to 
continual  change,  so  that  the  hill  of  today  may  become  the 
valley  of  the  future.  The  falling  rains  and  the  driving 
winds  tear  down  the  earth's  surface  at  one  point  and  build 
it  up  in  another.  This  process  is  known  as  erosion.  No 
one  has  expressed  the  importance  of  this  process  in  words 
finer  than  the  following: 

"The  hills  are  shadows,  and  they  flee 
From  form  to  form,  and  nothing  stands ; 
They  melt  like  mists,  the  solid  lands, 
Like  clouds  they  shape  themselves  and  go." 
Naturally  erosion  is  most  active  on  the  softer  rocks, 
and  on  these  the  valleys  are  usually  located.     The  harder 
rocks  give  us  the  elevations.     The  differences  in  hardness 
of  the  individual  layers  of  a  rock  are  clearly  shown  in  any 
exposure.     The  harder  layers  project  as  ribs  or  knobs ;  the 
softer  layers  are  worn  away  and  leave  pits,  cavities,  and 

irregular  depressions. 

Topography  depends  to  a  great  extent  on  the  attitude 
of  the  underlying  rocks.  In  regions  of  horizontal  rock, 
the  harder  portions  project  above  the  surrounding  country 
as  flat-topped  elevations  of  small  or  large  surface  area, 
known  respectively  as  "buttes"  and  "mesas".  In  regions 
of  inclined  rocks,  the  harder  layers  form  long  narrow 
ridges  which  we  speak  of  as  "hog  backs". 


40 


POPULAR  OIL  GEOLOGY. 


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V.   Stratigraphic  Geology 

The  part  of  geological  science  that  deals  with  the 
order  of  succession  of  rock  layers,  and  attempts  to  deter- 
mine their  relative  ages,  is  known  as  Stratigraphic  Geol- 
ogy. In  attempting  to  compare  or  "correlate"  rocks  one 
of  three  methods  can  be  followed : 

Tracing  Outcrops. 

Occasionally  it  happens  that  a  particular  bed  of  rock, 
such  as  a  limestone,  yields  a  more  or  less  continuous  expo- 
sure or  "outcrop"  on  the  earth's  surface,  which  can  be  fol- 
lowed for  a  considerable  distance,  and  which  will  hence 
serve  as  a  basis  for  comparison.  This  method  is,  of  course, 
subject  to  limitations.  The  time  required  to  trace  a  forma- 
tion from  a  known  field  to  the  one  in  question  may  be  so 
great  as  to  make  its  cost  prohibitive.  There  is  also  the 
probability  that  the  outcrops  may  be  covered  for  a  consid- 
erable area.  This  is  generally  the  case. 

Comparing  Lithological  Characteristics. 

A  known  formation  may  be  characterized  by  certain 
physical  properties,  such  as  its  color,  its  hardness,  its 
characteristic  layering  or  bedding,  and  its  composition. 
A  similar  formation  in  a  different  locality  may  represent 
the  same  layer.  This  is  frequently  assumed,  but  is  not 
necessarily  true,  because  experience  has  shown  that  no 
matter  how  peculiar  and  unusual  certain  characteristics 
may  appear  to  be,  they  may  recur  any  number  of  times. 
The  comparison  of  successive  layers  of  rocks,  of  their  char- 
acteristics and  thicknesses  is  a  more  valuable  method  of 
correlation.  An  illustration  will  make  this  clear.  In  a 
known  field  we  find  a  conglomerate  three  hundred  feet 
thick  succeeded  by  eight  hundred  feet  of  red  sandstone, 
which  in  turn  is  followed  by  eleven  hundred  fifty  feet  of 
alternating  red  and  green  shales.  Some  distance  away  we 
find  a  succession  of  rocks  similar  in  characteristics  and 
thickness.  Therefore,  we  may  argue  with  some  safety 

41 


42  POPULAR  OIL  GEOLOGY. 

that  these  two  groups  are  probably  equivalent  in  age.  This 
method,  while  capable  of  more  general  application  than 
the  first,  is  also  subject  to  limitations.  The  liability  of 
change,  both  in  the  thicknesses  and  characteristics  of  the 
rock  layers,  must  be  considered.  In  the  case  of  widely 
separated  fields,  the  individual  rock  layers  may  have 
changed  so  much  as  to  make  this  method  of  correlation 
infeasible. 

Use  of  Fossils. 

About  one  hundred  years  ago  the  British  civil  engi- 
neer, William  Smith,  discovered  the  fact  that  each  layer 
of  rock  carries  fossils  which  are  characteristic,  and  .that 
these  fossils  can  be  used  to  prove  that  widely  separated 
rocks  are  of  the  same  geological  age.  This  discovery  en- 
abled us  to  make  the  geological  time  table,  especially  after 
the  doctrine  of  evolution  had  been  worked  out  in  detail. 

Evolution. 

The  theory  of  evolution  teaches  us  that  the  various 
types  of  animals  and  plants  have  developed  by  descent  from 
pre-existing  types.  In  general,  progress  has  been  from  the 
simpler  towards  the  more  highly  organized  and  ^complex 
types.  Indications  are  that  all  animals  and  plants  are  the 
descendants  of  a  very  few  simple  organisms  not  unlike  the 
simpler  protozoans.  The  various  living  types  of  animals 
and  plants  do  not  form  a  series  showing  a  complete  grada- 
tion from  the  most  simple  to  the  most  complex.  Instead, 
•  they  represent  a  genealogical  tree,  the  branches  of  which 
exhibit  very  different  degrees  of  divergence  from  the 
parent  stock.  Indeed,  many  of  these  branches  are  now 
known  only  by  their  fossil  remains.  Close  resemblance 
among  animal  groups,  such,  for  instance,  as  that  between 
man  and  the  anthropoid  ape,  does  not  rftean  descent  of  one 
from  the  other,  but  indicates  a  common  ancestral  stock. 

Geology  has  proven  the  fact  that  every  species  of  ani- 
mal and  plant  lives  only  for  a  limited  time  on  earth,  then 
it  dies  out,  and  once  extinct  never  returns.  If  we  arrange 
the  sedimentary  rocks  in  a  column  with  the  oldest  at  the 


POPULAR   OIL   GEOLOGY. 


43 


bottom  and  the  youngest  on  top,  similar  to  the  chronolog- 
ical table  given  later,  we  will  find  that  each  species  of 
animal  or  plant  has  a  certain  vertical  range  which  repre- 
sents its  period  of  existence  on  earth.  The  vertical  range 
of  species  is  not  the  same  in  all  parts  of  the  earth.  A 
particular  animal  has  its  origin  in  some  definite  locality 
and  spreads  laterally  from  there  over  the  surface  of  the 
earth  and  then  dies  out.  It  does  not  necessarily  survive 
last  in  the  area  of  origin. 


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Space    Distribution 


Figure  8. 


Diagram   to  show  space  and  time  distribution 
of  a  fossil. 


The  accompanying  diagram  illustrates  this  fact  graph- 
ically. The  horizontal  line  represents  distance  on  the 
earth's  surface;  the  vertical  line  represents  time;  1,  2,  3, 
4,  etc.,  represent  tlie  sedimentary  rocks  deposited  in  order. 
A  is  the  point  of  origin  of  a  particular  animal  which 
spreads  laterally  and  with  different  velocities  to  the  points 
E  and  D,  and  eventually  disappears  at  the  point  C.  The 
shaded  area,  therefore,  gives  us  both  the  time  distribution 
and  the  space  distribution  of  this  species  on  the  earth. 


44  POPULAR  OIL  GEOLOGY. 

If  we  examine  the  rocks  deposited  at  the  locality  A,  E, 
or  C,  we  will  find  this  species  characterizing  rocks  of 
slightly  different  age  because  of  differences  in  the  time  of 
appearance  and  of  disappearance  of  this  species.  To  make 
a  fossil  especially  useful  for  correlation  it  should  have  a 
small  vertical  range,  that  means  short  life  on  earth ;  and 
in  addition  it  must  be  easily  and  rapidly  distributed  over 
a  large  area.  Ordinarily  we  use  not  a  single  fossil,  but  a 
whole  collection  of  fossils  as  a  basis  of  comparison.  The 
group  of  animal  fossils  characterizing  a  formation  is 
known  as  a  "fauna" ;  the  group  of  plant  fossils,  as  a 
"flora". 

Preservation  of  Animal  Remains. 

Fossils  are  the  impression  or  remains  of  animals 
and  plants  entombed  in  the  rocks  by  natural  causes.  Pres- 
ervation depends  on  the  character  of  the  organism.  Only 
those  with  bony  structures  are  capable  of  preservation.  It 
will  also  be  evident  that  the  home  of  the  animal  has  a 
great  effect  on  liability  of  preservation.  Water,  and  espe- 
cially marine  animals,  are  far  more  likely  to  leave  a  fossil 
than  land  animals.  The  fleshy  portion  is  never  preserved. 
The  only  exception  to  this  rule  are  elephants  that  have 
been  found  frozen  in  the  arctic  gravels  in  northern  Siberia, 
in  which  case  the  preservation  of  the  flesh  was  due  to 
excessive  cold.  Under  ordinary  conditions  only  the  bones 
and  the  shells  can  form  fossils.  Occasionally  bones  or 
shells  are  preserved  in  their  original  condition.  More  fre- 
quently, however,  they  have  been  replaced  by  some  mineral 
matter.  This  simply  means  that  the  bone  has  gradually 
gone  into  solution  and  that  simultaneously  for  each  parti- 
cle of  bone  dissolved,  a  particle  of  mineral  matter  has  been 
deposited. 

There  occur  quite  commonly  in  the  rocks  eccentric 
shaped  bodies  which  are  the  result  of  water  circulation  and 
the  deposition  of  mineral  matter  about  some  nucleus  such 
as  a  leaf  or  a  small  fossil.  These  bodies  which  we  call 
concretions  often  simulate  in  shape  animals  of  various 
sorts,  the  legs  and  arms  of  human  beings  and  almost  any- 


POPULAR  OIL  GEOLOGY.  45 

thing  else,  provided  the  imagination  of  the  observer  is  vivid 
enough. 

Geological  History. 

The  sedimentary  rocks  are  deposited  in  a  systematic 
order  with  the  oldest  at  the  bottom  and  the  youngest  at 
the  top.  The  order  of  deposition  and  the  chronological  re- 
lationship of  rocks  has  been  worked  out  in  great  detail. 
The  systematic  study  of  the  rocks  and  of  their  succession 
enables  us  to  deduce  the  series  of  events  that  characterized 
the  past  history  of  the  earth.  For  example,  the  character 
of  the  rock  tells  us  the  conditions  under  which  it  accumu- 
lated. Thus  bright-colored  rocks  associated  with  salt  and 
with  beds  of  gypsum,  are  characteristic  of  deposition  in 
arid  or  semi-arid  regions  such  as  deserts.  The  preserva- 
tion of  mud  cracks,  of  the  tracks  of  animals,  of  ripple 
marks  in  the  sand,  all  tell  us  of  deposition  in  very  shallow 
water  exposed  at  intervals  to  the  drying  sun.  Very  pure 
sandstones,  made  up  of  uniform  sized  spherical  sand  grains 
and  characterized  by  a  very  eccentric  and  irregular  bed- 
ding, indicate  deposition  by  drifting  winds. 

The  succession  of  rocks  indicates  to  some  extent  the 
changes  on  the  earth's  surface.  In  the  present  day  the 
rain,  the  driving  wind,  and  the  flowing  water  all  tear 
down  the  earth's  surface  and  transport  the  fragmental  ma- 
terial through  creeks  and  rivers  into  the  sea.  Here,  as  a 
result  of  wave  action  and  of  shore  currents,  this  material 
is  washed,  sorted  and  deposited  according  to  size.  The 
coarsest  material  next  to  the  shore;  the  finest  a  consider- 
able distance  away,  out  in  the  quiet  water.  Thus  fringing 
the  ocean  shore,  we  expect  first,  a  zone  of  boulders  and 
gravel,  next,  a  zone  of  sand,  and  in  the  quieter  waters,  a 
belt  or  zone  of  mud.  Animal  life  is  especially  plentiful 
and  flourishing  in  the  clearer  water,  and  here  the  shells 
and  skeletons  accumulate  upon  death.  Applying  these 
principles,  we  may  argue  that  a  succession  of  rocks,  such 
as  conglomerates  at  the  base,  followed  in  order  by  sand- 
stone, shale  and  limestone,  all  grading  into  each  other, 
means  a  gradual  deepening  of  the  sea  over  that  point.  A 


4:0  POPULAE   OIL   GEOLOGY. 

succession  in  reverse  order  means  a  shallowing  of  the  sea. 
Thus  the  succession  of  the  strata  enables  us  to  work  out  the 
great  advances  and  recessions  of  the  sea  that  have  charac- 
terized the  past  history  of  the  North  American  continent. 
While  we  cannot  go  into  detail  at  this  point,  it  may  suf- 
fice to  state  that  the  American  continent  has  not  always 
been  of  the  same  size  it  is  today ;  that  it  has  been  subject 
to  profound  geographic  changes;  that  at  times  the  whole 
continent,  with  the  exception  of  northeastern  Canada,  was 
covered  by  ocean  water ;  that  a  number  of  times  it  emerged 
from  the  ocean  only  to  be  submerged  to  a  more  or  less  com- 
plete degree  afterwards. 

It  is  customary  to  divide  geological  time  into  larger 
divisions  known  as  eras,  and  smaller  divisions  known  as 
periods.  The  accompanying  table  shows  the  classification 
of  eras  and  periods  in  common  use  at  the  present  time. 
It  may  be  weir  to  note  that  the  kind  of  sedimentary  rock 
bears  no  relation  whatsoever  to  its  age.  Sandstones  or  any 
other  kind  of  rock  may  occur  in  any  geological  age. 

Geologic  Chronology  of  North  America. 

(Modified  after  Pirsson  and   Schuchert) 


Era 

Periods. 

Advances    in    Life. 

Dominant  Life. 

Recent. 

Rise    of    world    civili- 
zation. 
The  era  of  mental 
life. 

AGE  OF  MAN. 

Glacial  or 

Periodic    glaciation. 

Psychozoic 

Pleistocene. 

Extinction  of  great 
mammals. 

AGE    OP 
MAMMALS 
AND 
MODERN 
PLANTS. 

Tertiary  — 
Pliocene. 

Miocene. 

Transformation   of 
man-ape  into  man. 
Culmination   of  mam- 
mals. 

Oligocene. 

Appearance   of  higher 
mammals. 

Eocene. 

Vanishing  of  archaic 
mammals. 

POPULAR   OIL  GEOLOGY.  47 

Geologic  Chronology  of  North  America — Cont. 


Era 


Mesozoic 


Periods. 


Epi-mesozoic 
interval. 


Cretaceous — 
Lance. 


Montanian. 
Coloradian. 


Commanchean. 


Jurassic. 


Triassic. 


Advances  in  Life. 


Rise  of  archaic 
mammals. 


Extinction  of  great 
reptiles. 


Extreme  specializa- 
tion of  reptiles. 


Appearance    of    flow- 
ering  plants. 


Appearance    of   birds 
and   flying   reptiles. 


Appearance  of  dino- 
saurs. 


Dominant  Life. 


AGE 

OF 

REPTILES. 


Paleozoic 


Epi-paleozoic 
interval. 


Extinction   of  ancient 
life. 


Permian. 


Appearance  of  land 
vertebrates. 

Appearance   of   mod- 
ern  insects   and 
ammonites. 

Periodic   glaciation. 


Pennsylvanian. 


Appearance  of  primi- 
tive reptiles  and  in- 
sects. 


AGE 

OP 

AMPHIBIANS 

AND 
FERN   PLANTS 


Mississippian- 
Tennessian. 


Waverlian. 


Appearance  of  ancient 
sharks. 


Appearance  of  echino- 
derms. 


Devonian. 


Appearance  of  Am- 
phibians.    First 
known  land  floras. 


Silurian. 


Appearance  of   lung- 
fishes  and  scorpions 


AGE 

OF 

FISHES. 


48  POPULAR   OIL   GEOLOGY. 

Geologic  Chronology  of  North  America — Cont. 


Era 

Periods. 

Advances  in  Life. 

Dominant  Life. 

Ordovician  — 
Cincinnatian. 

Appearance  of  land 
plants  and  corals. 

Champlainian. 

Appearance    of   ar- 
mored  fishes. 

Paleozoic 

Canadian 
Ozarkian. 

Appearance  of  nau- 
tilids. 

AGE 

Cambrian  — 
Croixian. 

Appearance  of  shelled 
animals. 

OP  HIGHER 
SHELL  FISH 

Acadian. 

Dominance  of  trilo- 
bites. 

Waucobian. 

First  known  marine 
faunas. 

Keweenawan 

Animikian 

Dominant    life 
inferred. 

Late  Pro- 
terozoic 

Huronian. 

AGE     OF    PRIMI- 
TIVE MARINE 

INVERTE- 
BRATES. 

(Fossils  almost  un- 
known.    Delinea- 

Early  Pro- 
terozoic 

Ep-algonian 
interval. 

Sudburian. 

this  age  indefi- 
nite.) 

Ep-archaeozoic 
interval. 

AGE  OF 
UNICELLULAR 

ozoic 

Laurentian. 

LIFE. 
Protozoa    and    pro- 

Greenville. 

tophyta. 

The   unrecoverable   beginning  of  Earth  History. 
COSMIC  HISTORY. 


POPULAR  OIL  GEOLOGY.  49 

Stratigraphic  Distribution  of  Oil  and  Gas. 

The  known  oil  and  gas  fields  are  not  confined  to 
rocks  of  any  one  particular  age.  No  commercial  accumu- 
lations have,  however,  been  found  in  rocks  older  than  the 
Cambrian;  therefore,  any  area  of  Proterozoic  or  Archaeo- 
zoic  rocks  can  at  once  be  excluded  as  a,  possible  oil  pro- 
ducer. The  most  important  geological  ages  from  the 
standpoint  of  production  are  given  in  the  following  table. 
Wherever  a  state  is  given  more  than  once,  the  more  im- 
portant production  is  given  in  capital  letters: 

Tertiary : 

CALIFORNIA. 

TEXAS  and  LOUISIANA. 

MEXICO. 

Cretaceous : 

WYOMING. 

COLORADO. 

Texas,  Corsicana. 

LOUISIANA,  Caddo,  Homer. 

California. 

Mexico. 

Commanchean,  Lower  Cretaceous: 
Oklahoma,  Medill. 
Wyoming,  Big  Horn  Basin  (in  part). 

Pennsylvanian : 

TEXAS,  Electra,  Ranger,  Burkburnett. 

Wyoming,  Lander. 

Pennsylvania,  West  Virginia,  Ohio,  Kentucky,  Indiana, 

Illinois,  all  in  part. 

OKLAHOMA-KANSAS. 

Mississippiari : 

ILLINOIS. 

PENNSYLVANIA. 

WEST  VIRGINIA. 

OHIO. 

INDIANA. 

KENTUCKY. 

Devonian: 

PENNSYLVANIA. 
WEST  VIRGINIA. 
OHIO. 

NEW  YORK. 
ONTARIO. 


50  POPULAR  OIL  GEOLOGY. 

Silurian : 

New  York. 
Ontario. 

Ordovician : 

OHIO-INDIANA. 
Kentucky. 
New  York. 
Ontario. 

Cambrian : 

New  York. 
Newfoundland. 
New  Brunswick. 

Tertiary  rocks  yield  over  50  per  cent  of  the  world's 
production  of  oil.  The  most  important  foreign  producing 
fields,  such  as  Galicia,  the  Dutch  East  Indies,  Peru,  Trini- 
dad, Russia  and  Roumania,  are  in  Tertiary  rocks.  Paleo- 
zoic rocks  are  important  producers  in  North  America  only. 
It  will  be  noted  that  Jurassic,  Triassic,  and  Permian  rocks 
are  non-productive  in  North  America.  This  is  due  to  the 
fact  that  they  represent  in  large  part  deposition  in  interior 
basins  under  conditions  of  semi-aridity.  As  a  result  they 
are  very  poor  in  organic  remains,  and  because  of  this  fact 
they  are  unfavorable  to  oil. 


POPULAR  OIL  GEOLOGY. 


51 


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VI.   The  Arrangement  and  Structures 
of  Rocks 

Structural  geology  deals  with  the  arrangement  and 
attitude  of  rocks  in  the  Earth's  surface.  From  the  stand- 
point of  the  oil  geologist  it  is  the  most  important  branch 
of  geological  science. 

We  have  already  seen  that  the  sedimentary  rocks  at 
the  time  of  formation  are  deposited  in  parallel  layers  or 
strata  that  are  more  or  less  horizontal.  We  may  find  them, 
however,  standing  on  edge  and  inclined  in  all  possible 
directions  as  a  result  of  some  disturbance  since  the  time 
of  their  deposition. 

Dip  and  Strike. 

The  attitude  or  position  of  a  stratum  is  a  geological 
feature  of  prime  importance  and  one  that  must  be  recorded. 


Figure  10.    Dip  and  Strike. 

This  is  done  by  observing  the  dip  and  strike.  The  dip  is 
the  inclination  of  the  bed  to  a  horizontal  plane.  The 
strike  is  the  bearing  of  the  line  of  intersection  of  a  hori- 
zontal plane  and  the  plane  of  the  stratum.  The  direc- 
tions of  dip  and  strike  are  at  right  angles  to  each  other. 
The  strike  is  always  expressed  by  compass  directions,  such 
as  North  40°  West  (K  40°  W.),  or  South  12°  East 
(S.  12°  E.).  The  dip  angle  varies  of  necessity  f* 
for  a  horizontal  bed  to  90°  for  a  vertical  one.  D^ 
strike  are  frequently  recorded  on  maps  by  a  symbol.  Inus, 
a  straight  line  is  drawn  in  the  correct  direction  of  the 

52 


POPULAR   OIL   GEOLOGY.  53 

str  and  at  right  angles  a  shorter  line  is  drawn  in  the 
direction  of  dip.  The  direction  of  the  strike  line  indi- 
cates the  true  bearing  of  the  strike.  The  dip  line  indi- 
cates the  bearing  of  the  dip  but  not  its  amount,  conse- 
quently it  is  customary  to  mark  down  the  value  of  the  dip 
angle  on  the  symbol. 

Outcrops. 

In  order  to  work  out  the  structure  of  rocks  and  to 
determine  dips  and  strikes,  it  is  necessary  to  locate  and 
study  outcrops;  that  is,  exposures  of  bed  rock  at  the  earth's 
surface.  When  the  surface  is  horizontal,  the  outcrop  of 
the  stratum  gives  the  direction  of  strike.  This  is  not  true, 
however,  in  the  case  of  inclined  layers  of  rock  that  cross 
rugged  country  with  high  hills  and  deep  valleys.  Here 
the  bearing  of  the  outcrop  and  the  strike  of  a  stratum  may 
diverge  widely,  becaus'e  the  outcrop  deviates  from  a  straight 
line  when  crossing  points  of  different  elevation.  Thus,  if 
a  bed  dips  upstream,  the  outcrop  travels  upstream  when 
crossing  a  valley ;  if  the  bed  dips  downstream,  the  outcrop 
travels  downstream.  The  amount  of  this  deviation  or 
travel  is  a  function  of  the  angle  dip  and  of  the  depth  of 
the  valley.  In  many  cases  this  enables  us  to  calculate  the 
dip  and  strike  when  no  direct  observation  is  feasible. 
Thus,  the  flatter  the  angle  of  dip  the  greater  the  travel  of 
outcrop  up  or  down  stream ;  the  steeper  the  angle,  the  less 
the  travel.  Vertical  strata  show  no  travel. 

Folds. 

Frequently  we  find  the  outcrops  of  certain  beds  re- 
peated in  such  a  way  as  to  suggest  that  strata  of  rocks 
in  the  earth's  crust  have  been  folded  in  nature  much  like 
we  fold  sheets  of  paper  between  our  fingers.  Such  folding 
is  a  common  characteristic  of  oil  fields. 

kinds  of  folds  may  be  recognized : 
Anticlines, 
Synclines,  and 
Monoclines  (or  homoclines). 


POPULAR   OIL  GEOLOGY. 


Figure  11.  Various  types  of  Folds.  1.  Symmetric  Anticline. 
2.  Asymmetric  Anticline.  3.  Overturned  Anticline.  4.  Symmet- 
ric Syncline.  5.  Asymmetric  Syncline.  6.  Overturned  Syncline. 


POPULAR   OIL  GEOLOGY.  55 

The  anticline  is  an  upfold  in  the  strata  or  an  arch. 
The  Syncline  is  a  downfold  or  a  trough.  The  Monocline 
is  a  stepfold,  or  a  flexure  in  a  single  direction  only.  The 
term  homocline  has  also  been  applied  to  a  number  of  fo>r^ 
mations  that  dip  in  one  direction  only. 

Degree  of  Folding. 

Folding  exhibits  various  degrees  of  intensity.  All 
gradations  from  very  gentle  rock  waves  to  intricately 
twisted  and  complex  crumples  are  shown.  Simple  and 


Figure  12.     Monocline. 

gentle  folding  is  most  characteristic  of  oil  regions.  Com- 
plex, intricate  folding  is  unfavorable  in  general  to  oil  ac- 
cumulation. Anticlines  and  synclines  are  usually  com- 
bined in  a  series  of  parallel  folds  of  wavelike  character, 
with  the  anticlines  at  the  crests  and  the  synclines  at  the 
troughs.  Both  occur  in  a  variety  of  forms.  They  may 'be 
low  and  broad,  or  acute  and  sharply  compressed.  They 
may  be  horizontal,  vertical,  or  inclined  in  position. 

The  amount  of  folding  is  roughly  measured  by  the 
difference  in  elevation  of  the  same  layers  of  rock  between 
the  lowest  part  in  the  syncline  and  the  highest  part  in  the 
anticline.  This  varies  from  a  few  feet  to*  several  miles. 
In  Wyoming  oil  fields  this  is  usually  large,  and  varies 
from  several  hundred  feet  to  one  mile.  In  Oklahoma  and 
Illinois,  this  is  usually  less  than  two  hundred  feet. 


56  POPULAR  OIL  GEOLOGY. 

Nomenclature  of  Folds. 

The  sides  of  the  folds  are  known  as  limbs.  The  axis 
is  the  direction  of  elongation.  The  anticlinal  axis  is  the 
highest  part  of  the  anticline,  or  its  crest.  The  axis  of  a 
syncline  is  the  bottom  of  the  trough.  Folds  are  symmetri- 
cal or  unsymmetrical,  depending  on  whether  or  not  the 
dip  of  the  limbs  from  the  axis  is  equal  in  opposite  direc- 
tions. Folds  are  horizontal  when  the  axis  is  horizontal. 
Folds  with  an  inclined  axis  are  plunging  or  pitching  folds. 
Various  folds  are  indicated  by  the  dip  and  strike  symbols 
in  the  accompanying  figures. 

x      \  ^     "\        '     ^ 

\      \         >          ;        <  } 

\        x        \  \ 

x       x      x^^         ^    J 

dnf/c/Sste 


*  /*"\  /"% 

/        /  /  \        \ 

/       /  /         *  i          \ 

/       /  /           *                      \ 

/        /  >              *  ]               \ 

/  '           ^  ^           \ 


Figure  13.    Various  structures  as  represented  by  their 
dip  and  strike  symbols. 

Composite  Folds. 

Two  types  of  folds  of  extreme  importance  to  an  oil 
man  are  dome  folds  and  basin  folds.  Both  may  be  con- 
ceived of  as  composite  folds,  consisting  of  two  folds  cross- 
ing at  right  angles.  In  domes,  or  quaquaversal  folds,  the 
rocks  have  the  attitude  of  an  inverted  bowl  and  dip  away 


POPULAR   OIL  GEOLOGY. 


57 


in  all  directions  from  the  center.  In  Basin,  or  centro- 
clinal  folds,  rocks  are  arranged  in  the  shape  of  a  natural 
basin  and  hence  dip  into  the  center  of  the  fold. 

Domes  and  Basins  also  have  axes  corresponding  to 
the  axes  of  anticlines  and  synclines.  The  axis  of  a  dome 
marks  the  highest  part  and  the  line  of  elongation  of  the 
fold.  The  highest  point  on  the  axis  is  the  apex. 

Faults. 

In  many  regions  we  find  that  the  rocks  have  been 
fractured  and  broken  on  an  extensive  scale,  and  that  the 
broken  parts  have  been  displaced  with  respect  to  each  other. 
Such  displacement  on  opposite  sides  of  a  fracture  or  fis- 
sure, is  a  fault.  The  fracture  is  the  fault  plane.  This  is 
usually  inclined.  The  two  sides  of  the  fault  are  known  as 
the  footwall  and  hanging  wajl,  respectively  (see  figure  14). 

According  to  the  character  of  the  motion  we  recognize 
two  great  classes  of  faults :  normal  faults  and  thrust  faults. 


Figure  14.     Normal  Fault. 


Normal  Faults. 


These  usually  have  steep  dipping  fault  planes  and  are 
produced  by  the  tension  or  stretching  of  rocks.  In  these, 
the  hanging  wall  moves  down  with  respect  to  the  footwall. 


58 

Thrust  Faults. 


POPULAR   OIL  GEOLOGY. 


The  majority  of  thrust  faults  have  flat,  dipping  fault 
planes.  They  are  most  common  in  regions  of  intricate  and 
complex  folding.  In  these  faults,  the  hanging  wall  moves 
up  over  the  footwall.  They  are  produced  by  lateral  press- 
ure and  the  crowding  of  rocks  over  each  other. 


Displacement. 


Figure   15.     Thrust   Fault. 


The  actual  amount  of  motion  in  the  fault  plane  is  the 
displacement.  This  may  vary  from  a  fraction  of  an  inch 
to  several  miles.  Normal  faults  are  most  common  in  oil 
fields.  These  usually  have  displacements  of  a  few  hundred 
feet  or  less.  Complex  faulting  on  a  large  scale  is  unfavor- 
able to  oil  accumulation. 


Figure  16.     Apparent  change  in  character  of  rocks  due 
to  faulting  shown  by  Well  No.  2. 

(U.  S.  Geol.  Sur.) 


POPULAR   OIL  GEOLOGY. 


59 


60  POPULAR  OIL  GEOLOGY. 

Unconformities. 

The  sedimentary  rocks  are  deposited  in  a  regular  and 
systematic  order.  Each  stratum  represents  a  definite  time 
interval;  all  collectively  represent  a  continuous  space  of 
time.  The  regular  succession  of  rocks  may  be  broken  or 
interrupted.  For  example,  after  the  deposition  of  marine 
strata  there  may  be  an  emergence  of  the  continent  from 
the  ocean,  which  exposes  the  recently  formed  strata  to  ero- 
sion. These  may  be  folded  and  faulted  and  eroded  into 
hills  and  valleys.  Subsequently  the  continent  may  again 
be  submerged  under  the  ocean  and  new  deposits  may  be 
laid  down  on  the  dissected  surface  of  the  older  series.  The 
younger  beds,  therefore,  do  not  conform  to  the  older  rocks 
below.  A  surface  of  contact  of  this  nature  is  an  Uncon- 
formity. 

The  Sedimentary  Rocks  record  Earth  history.  The 
rocks  above  and  below  the  unconformity  record  periods  of 
time  perhaps  less  extensive  than  the  duration  represented 
by  the  unconformity.  This  marks  a  lost  time  interval  sim- 
ilar to  a  chapter  torn  out  of  a  novel.  Unconformities  may 
be  clearly  shown  by  differences  in  attitude  of  rocks  indi- 
cating that  the  older  series  of  rocks  were  tilted  and  folded 
and  eroded  preceding  the  deposition  of  the  younger  series. 
They  are  quite  important  and  their  influence  must  be  care- 
fully considered  in  certain  oil  fields. 


VII.   Reservoirs  of  Oil  and  Gas 

Any  rock  that  is  capable  of  containing  oil  and  gas 
in  commercial  quantities  is  known  as  a  "reservoir".  The 
most  common  types  of  reservoir  rocks  are:  first,  sand- 
stones; second,  limestones;  and  third,  shales.  These  will 
be  discussed  briefly. 

Sandstones. 

Sandstones  are  the  most  common  type  of  reservoir 
rocks.  The  amount  of  oil  that  any  sandstone  may  carry  is 
determined  by  the  number  and  size  of  openings  it  con- 
tains, or,  in  other  words,  its  porosity.  This  depends  on 
the  size  and  shape  of  the  grains,  and  on  the  degree  of 
cementation.  The  greatest  amount  of  pore  space  is  pos- 
sessed by  the  rock  that  has  spherical  grains  of  uniform  size ; 
the  least  amount  of  pore  space,  by  the  sandstone  made  up 
of  unassorted  angular  grains.  Cement  is  quite  important 
in  determining  porosity  because  it  clogs  up  the  interstices 
between  the  grains  to  a  greater  or  less  degree.  A  well- 
cemented  sandstone  is  hard;  a  loosely  cemented  one,  soft 
and  friable,  that  is,  it  may  be  crumbled  in  the  hands. 
Hard,  well-cemented  sandstones  form  the  reservoir  rocks 
in  the  Appalachian  oil  fields,  in  Illinois,  Kansas  and  Okla- 
homa. Soft,  friable  sandstones  form  the  reservoirs  in  Wyo- 
ming, Colorado,  and  in  northern  Texas  and  Louisiana. 
The  oil.  production  from  California,  Russia,  Galicia,  Rou- 
mania,  and  Peru  comes  from  unconsolidated,  loose  beds 
of  sand. 

"According  to  the  amount  of  pore  space,  we  speak  of 
"close"  or  "tight"  sands,  which  mean  those  of  low  poros- 
ity, and  of  "open"  sands,  those  of  high  porosity.  The 
amount  of  pore  space  of  any  sandstone  can  readily  be 
determined  by  saturating  the  dry  rock  completely  with 
water  and  noting  the  amount  of  water  absorbed.  The 
porosity  so  determined  is  known  as  theoretical  porosity. 
This  varies  from  one-half  percent  in  the  case  of  quartzite, 
to  30  percent  in  the  case  of  sand.  The  general  average 

61 


62 


POPULAR   OIL   GEOLOGY. 


Figure  18.     Diagram  illustrating  the  effect  of  size  of  grain  and 
method  of  packing  on  porosity. 


POPULAR  OIL  GEOLOGY.  63 

is  10  percent.  This  ia  the  equivalent  of  seven  hundred 
seventy-six  barrels  of  oil  per  acre-foot.  This  means  that 
a  sandstone  bed  one  foot  in  thickness  and  extending  over 
one  acre,  will  contain  seven  hundred  seventy-six  barrels 
of  oil.  We  must,  however,  carry  in  mind  the  fact  that 
there  is  a  difference  between  theoretical  and  practical  po- 
rosity. While  the  theoretical  porosity  may  be  10  per- 
cent, the  practical  porosity  is  far  less,  because  ordi- 
narily only  from  50  percent  to  75  percent  of  the  oil  in 
the  sand  can  be  recovered.  Thus  in  the  Appalachian  fields 
the  practical  porosity  is  4.5  percent,  which  is  equiv- 
alent to  three  hundred  fifty  barrels  of  oil  per  acre-foot. 
At  Glennpool,  in  Oklahoma,  the  practical  porosity  is 
6.5  percent,  which  means  that  five  hundred  thirty-five 
barrels  of  oil  can  be  extracted  for  each  acre-foot  of  sand. 
Extraction  is  favored  by  high  porosity,  by  large  and  con- 
nected openings,  and  by  low  viscosity  of  the  oil.  All  of 
these  factors  promote  ready  circulation  and  easy  flow. 
In  the  case  of  uncoiisolidated  sands,  even  a  highly  viscous 
oil  may  flow  readily  because  of  the  fact  that  it  will  carry 
the  sand  along  with  it.  Thus  in  some  of  the  Russian  and 
Californian  fields,  more  than  50  percent  of  The  material 
flowing  out  of  the  well  is  sand. 

In  color  oil  sands  vary  decidedly.  Usually  they  are 
darker  in  color  than  the  barren  sands.  Asphalt  oils  leave 
yellow  to  brown  stains  on  the  rock  and  impart  to  it  the 
odor  of  petroleum.  The  paraffin  base  oils  are  so  light  and 
evaporate  so  readily  that  frequently  no  trace  is  visible  in 
the  outcropping  oil  sands. 

Test  for  Oil  in  Sands. 

The  presence  of  inspissated  hydrocarbons  in  an  out- 
cropping sand  can  be  determined  by  sampling  the  outcrop, 
crushing  the  rock  and  treating  a  tablespoonful  of  the  frag- 
ments with  ether  in  a  well-corked  bottle  for  half  an  hour. 
Any  hydrocarbons  present  will  go  in  solution.  If  subse- 
quently the  liquid  be  poured  off  into  a  white  china  dish, 
it  will  evaporate 'rapidly  and  leave  behind  a  ring  of  oil. 
This  will  be  greenish  amber  to  pale  brown  in  color  in  the 


POPULAR   OIL  GEOLOGY. 


case  of  very  high-grade  paraffin  base  oils,  or  dark  brown 
to  black  in  color  in  the  case  of  asphalt  base  oils. 

Shape  of  Reservoir. 

Certain  sandstones  occur  in  well-defined  strata  that 
are  more  or  less  constant  in  thickness,  and  that  extend 
over  very  large  areas.  An  example  of  such  is  the  Dakota 
sandstone  which  is  known  to  extend  over  an  area  of  two 
thousand  by  one  thousand  miles.  More  frequently,  sand- 
stones are  lenticular  in  structure.  They  are  limited  in 
areal  distribution  and  thin  out  or  "pinch  out"  laterally. 
The  entire  sandstone  bed  must  not  be  thought  of  as  being 


WELL  NO.  I 


WELL  NO.  2 


WELLNO.3 


Figure  19.    Lenticular  sands  and  their  effect  on  wells. 

(U.  S.  Geol.   Sur.) 

a  reservoir.  There  are  certain  portions  that  may  be  in- 
capable of  holding  either  oil  or  water  because  of  the  fact 
that  they  are  very  tightly  cemented,  or  perhaps  made  up 
of  excessively  fine  grains.  The  reservoir  is  confined  to 
the  porous  part  of  the  sandstone  where  the  grains  are 
coarser  and  consequently  the  interstitial  cavities  are  larger, 
or  where  the  cement  is  poorer  and  does  not  completely  fill 
the  room  between  the  grains.  The  accompanying  sketch 
map  shows  a  small  area  underlain  by  oil  sands.  The  reser- 
voirs are  indicated  by  shading.  It  will  be  noticed  that  the 
oil  pools  are  restricted  laterally,  not  by  the  structure  nor 
by  the  extent  of  the  sandstone,  but  by  the  porous  layers 
capable  of  acting  as  reservoirs. 


POPULAR  OIL  GEOLOGY. 


65 


Figure  20.    Lenticular  layers  in  oil  sands  shown  by  shading. 
Cross  hatching  shows  oil,  dotting  gas,  broken  lines  water. 

Limestones. 

The  limestones  that  we  meet  with  in  oil  fields  repre- 
sent the  fragments  of  the  shells  of  animals  and  the  skele- 
tons of  corals,  which  have  been  compacted  into  rock.  Fos- 
sils are  plainly  visible  in  many  limestones.  In  many 
others  they  are  very  indistinct  and  may  be  completely  de- 
stroyed. Limestones  are  essentially  calcium  carbonate. 
When  pure  they  are  ordinarily  unfavorable  as  oil  reser- 
voirs. Certain  limestones,  known  as  dolomitic  limestones, 
or  dolomites,  carry  varying  amounts  of  magnesium.  Such 
contain  oil  or  gas  in  a  number  of  prominent  fields.  While 
there  are  differences  of  opinion  as  to  the  origin  of  the 


66  POPULAE   OIL  GEOLOGY. 

dolomites,  it  is  generally  conceded  that  magnesium  carbon- 
ate, which,  is  brought  into  the  limestone  by  circulating 
solutions,  takes  the  place  of  a  certain  number  of  calcium 
carbonate  molecules.  Since  the  specific  gravity  of  magne- 
sium carbonate  is  greater  than  that  of  calcium  carbonate, 
less  space  is  required  for  each  magnesium  carbonate  mole- 
cule, and  as  a  result  we  have  a  shrinkage  of  volume  in  the 
original  rock.  The  shrinkage  is  equal  to  12.30  percent. 
Thus  if  one  hundred  cubic  feet  of  limestone  has  one-half 
of  its  molecules  of  calcium  carbonate  replaced  by  magne- 
sium carbonate,  the  resulting  rock  will  have  12.30  cubic 
feet  of  pore  space.  These  openings  serve  as  receptacles  for 
oil  and  for  gas.  Dolomitic  limestones  form  the  reservoir 
rock  of  the  Lima  field  of  Ohio  and  Indiana,  of  Spindle 
Top  and  other  fields  in  Texas,  and  of  Maiden-i-Napthun  in 
Persia.  The  oils  in.  limestone  are  usually  of  asphalt  base 
and  are  high  in  sulphur  and  in  nitrogen. 

Pure  limestones  are  quite  easily  soluble.  Conse- 
quently circulating  water  will  dissolve  out  caves  and  chan- 
nels. The  extensive  cave  systems  of  Mammoth  Cave  in 
Kentucky  and  of  Wind  Cave  in  South  Dakota  are  famil- 
iar examples.  Water  channels  of  this  sort  may  occasionally 
act  as  reservoirs.  This  is  true  in  certain  of  the  Mexican 
fields.  Oil  will  flow  very  readily  in  such  reservoirs.  Con- 
sequently wells  of  great  capacity  and  usually  short  life  may 
be  expected. 

Shales. 

The  older  geologists  emphasized  the  importance  of 
rock  fractures  and  fissures  as  oil  containers,  and  believed 
these  to  be  far  mpre  important  than  the  interstitial  cavi- 
ties between  sand  grains  or  the  shrinkage  cavities  in  lime- 
stones. At  the  present  time  this  idea  is  applied  to  but  a 
few  pools.  For  example,  at  Florence,  Colorado,  oil  is 
found  in  open  fissures  and  fractures  in  a  thick  bed  of  shale. 
Several  other  localities,  such  as  West  Salt  Creek,  in  Wyo- 
ming, and  a  few  areas  in  Pennsylvania,  show  a  similar 
type  of  accumulation.  Generally,  however,  it  may  be  said 
that  such  occurrence  is  unimportant  and  unreliable. 


POPULAR   OIL   GEOLOGY. 


67 


>m«           0-  90 

halt  »0  I3S 

,nala  170  100 

'»drot*    190-  205 

halt  ZQS-  240 

imt  24O-  2«0 

£hol«  ?60-  330 

Lirnt  330-  3«0 

Shola  360-  4i6 

Sand  413-  43O 

Shalt  430-  340 

d  £40-  350 


oil 

Shale      630- 


Lim«      000-    900 


e  97O-  'OJi 

d  1025-1040 

Lirrx  1040-IOiO 

Shalt  1030-1015 


Shalt    I333-/400 

Lint*  i400- '303 
Shalt  1505-151* 
Sand  1325-1353 

Shalt    1333-  ITiO 


Shan     1890-2003 


L.rn*    C   03   *  190 


5/Mte     2 1 00- 29 10 

L.m«  2310-1370 
Shalt  IJ70-Z450 
Lim«  2430-2460 

5^>-Zo,*s«"*° 


TYPICAL   M£LLLOG 

Figure  21.     Map  of  the  Augusta  and  Eldorado  pools  in  Kansas 
and  typical  well  log. 

(After  Hager) 


68  POPULAR  OIL  GEOLOGY. 

Other  Rocks. 

The  above  include  all  important  reservoir  rocks,  al- 
though small  quantities  of  both  oil  and  gas  occur  occasion- 
ally in  crystalline  rocks.  At  the  recently  discovered  Thrall 
oil  field  in  Williamson  County,  Texas,  the  reservoir  rock 
is  a  basic  igneous  rock  known  as  limburgite.  It  o\ves  its 
porosity  in  large  part  to  extensive  alteration  by  circulating 
underground  water.  The  oil  and  gas  it  contains  are  de- 
rived from  the  surrounding  Cretaceous  sediments  with 
which  this  igneous  rock  is  interbedded. 

The  Enclosing  Beds  of  Reservoirs. 

Reservoir  rocks  must  be  retained  between  rocks  im- 
pervious to  the  circulation  of  oil,  -as,  without  these,  we 
could  expect  no  commercial  accumulation.  The  most  com- 
mon type  of  enclosing  beds  are  water-wet,  fine-grained 
rocks,  such  as  clays  and  shales.  Occasionally,  the  enclos- 
ing rocks  are  similar  to  the  reservoirs,  but  either  so  tightly 
cemented  or  so  excessively  fine-grained  as  to  make  the 
movement  of  oil  through  them  impossible. 


VIII.  The  Laws  of  Migration  and  Accumu- 
lation of  Oil  and  Gas 

In  the  preceding  discussion  we  concluded  that  oil  and 
gas  are  formed  by  the  distillation  of  plant  and  animal  re- 
mains which  are  buried  in  the  rocks  by  natural  causes  at 
the  time  of  tljeir  deposition.  Of  all  sediments,  muds  are 
most  prolific  in  organic  remains.  It  seems  highly  probable, 
therefore,  that  by  far  the  greater  part  of  oil  and  gas  was 
originally  formed  in  shales.  Since  neither  oil  nor  gas 
occur  in  any  great  quantity  in  this  rock,  we  are  driven  to 
the  conclusion  that  they  have  migrated  from  shale  and  have 
been  concentrated  in  rocks  more  suitable  as  reservoirs. 

Causes  of  Migration. 

A  number  of  different  causes  have  probably  been  act- 
ive in  forcing  such  migration,  chief  among  which  we  may 
mention  the  following: 

1.  Differences  in  specific  gravity  of  gas,   oil, 

and  water. 

2.  Head  of  ground  water. 

3.  Gas  pressure. 

4.  Rock  pressure. 

5.  Earth  movement, 

6.  Heat  gradient. 

7.  Capillary  attraction. 

Differences  in  Specific  Gravities. 

It  is  a  well-known  facf  that  gas  is  lighter  than  oil, 
and  oil  lighter  than  water.  Oil  and  water  are  not  miscible. 
Oil  floats,  therefore,  on  the  surface  of  the  water.  Conse- 
quently, wherever  oil  and  water  are  mixed  in  rocks  under 
the  earth's  surface  oil  should  be  on  the  top,  and  wherever 
water  moves  through  rocks,  oil  must  be  driveiuahead  of  it. 
Many  phenomena  tend  to  show  that  ground  water  is  seldom 
stagnant,  but  instead  is  subject  to  gentle  and  continuous 
circulation,  and  for  this  reason,  many  geologists  see  in  the 

69 


70  POPULAR   OIL  GEOLOGY. 

differences  of  the  specific  gravities  of  oil  and  water  the 
most  powerful  cause  of  oil  migration. 

Head  of  Ground  Water. 

The  water  in  the  rocks  of  the  earth's  crust  is  known 
as  ground  water,  or  underground  water.  This  water  is 
under  pressure  which  is  known  theoretically  as  "head". 
The  head  is  the  factor  determining  the  height  to  which 
water  will  rise.  "Head",  therefore,  causes  water  to  flow, 
and  fo;r  the  reasons  already  mentioned,  oil  and  gas  are 
driven  ahead  of  the  water  through  the  rocks.  In  many 
fields  the  head  of  the  ground  water  has  been  determined 
and  for  a  large  number  of  cases  proved  to  be  equivalent  to 
the  pressure  on  the  oil  and  gas  as  determined  in  the  wells. 
Thus  for  many  of  the  Ohio  fields  the  pressure  on  the  oil 
is  equivalent  to  the  head  of  water  standing  at  the  level  of 
Lake  Erie. 

Gas  Pressure. 

The  gas  associated  with  oil  is  frequently  under  very 
great  pressure.  Maxima  of  fifteen  hundred  pounds  to  the 
square  inch  have  been  recorded.  This  pressure  is  of  neces- 
sity exerted  in  all  directions  and  may  to  some  extent  force 
oil  to  move  through  rocks.  Gas  pressure  is  of  great  im- 
portance in  certain  oil  fields  because  it  may  be  sufficiently 
great  to  force  the  oil  through  the  well  up  to  the  surface 
of  the  earth  and  so  produce  flowing  wells  or  gushers.  It 
is  probably  not  a  very  important  cause  of  oil  migration. 
Gas  migrates  in  all  directions  far  more  easily  than  oil. 
Gas  fields,  therefore,  are  of  larger  extent  than  oil  fields, 
and  may  be  entirely  distinct  from  them. 

Rock  Pressure. 

Rocks  underneath  the  earth's  surface  are  under  pres- 
sure equivalent  to  the  weight  of  the  column  of  rocks  above 
them.  With  increasing  depth  this  pressure  may  be  so 
great  that  no  openings  can  exist,  and  that  the  rocks  will 
flow  like  wax.  Such  pressure  is  hydrostatic,  that  is,  sim- 
ilar to  pressure  under  water,  equal  in  all  directions.  Rocks 
under  such  pressure  are  said  to  be  in  the  zone  of  flowage. 


POPULAR  OIL  GEOLOGY.  71 

As  will  be  evident,  the  pressure  necessary  to  bring  about 
this  condition  will  vary  with  the  rocks.  Kocks  of  high 
crushing  strength,  such  as  well-indurated  sandstones,  re- 
quire a  pressure  equivalent  to  a  burial  of  several  miles; 
clay  shales  on  the  other  hand,  are  in  a  condition  of  flowage 
after  burial  of  three  hundred  feet  and  perhaps  less.  The 
effect  of  rocks  whose  pores  and  openings  are  saturated  with 
oil  or  water  will  be  similar  to  that  of  a  sponge  saturated 
with  water  and  subject  to  pressure.  The  liquid  and  lighter 
material  will  be  gradually  squeezed  out  and  forced  towards 
the  surface.  Rock  pressure  is  undoubtedly  a  very  potent 
cause  of  oil  migration,  especially  in  rocks  deeply  buried. 
Below  four  thousand  feet  it  is  probably  the  most  important 
cause  of  movement. 

Earth  Movements. 

Earth  movements,  such  as  folding  and  faulting  and 
tidal  deformations,  set  up  stresses  and  strains  in  the  in- 
terior of  the  earth  which  have  some  stimulating  effect  on 
oil  migration.  Their  importance  is  probably  very  slight, 

Heat  Gradient. 

As  we  descend  from  the  earth's  surface,  we  find  that 
the  temperature  increases  at  a  more  or  less  regular  rate 
of  1°  C  for  every  fifty  to  one  hundred  feet.  This  regu- 
larly increasing  temperature  may  have  a  slight  stimulating 
effect  on  circulation.  The  general  tendency  will  be  to 
drive  the  liquids  upward.  Its  importance  is  probably  very 
slight,  because  of  the  great  depth  required  for  an  effective 
temperature  increase.  Thus  a  burial  of  one  mile  is  only 
equivalent  to  a  temperature  increase  of  50°  to  100°  C. 

Capillary  Attraction. 

The  tendency  of  liquids  to  ascend  minute  openings 
and  pores,  such  as  those  in  sponges,  is  a  result  of  capillary 
attraction.  Any  opening  of  tube  shape  and  less  than  one- 
half  millimeter  (one-fiftieth  of  an  inch)  in  diameter  is  a 
capillary  opening.  Liquids  will  tend  to  rise  in  such  tubes 
against  the  effects  of  gravity.  The  height  of  such  rise  will 
depend  upon  the  nature  of  the  liquid,  the  size  of  the  tube, 


72  POPULAR  OIL   GEOLOGY. 

and  the  material  of  the  tube.  The  effective  pressure  that 
forces  liquids  to  ascend  such  tubes,  is  capillary  pressure. 
This  is  a  function  of  the  surface  tension  of  the  liquid  and 
the  attraction  between  the  liquid  and  the  tube.  The 
greater  the  surface  tension  the  greater  the  capillary  pres- 
sure, consequently  the  greater  the  tendency  to  enter  micro- 
scopic pores.  Water  has  a  surface  tension  three  times 
that  of  crude  oil.  Water,  therefore,  exerts  a  capillary 
pressure  three  times  as  great  as  that  of  crude  oil. 


Figure  22.  Rise  of  a  Water-Oil  emulsion  between  plates  of 
glass  as  a  result  of  capillary  attraction.  Cross-hatched  area  is 
oil.  Note  that  on  separating,  the  water  has  occupied  the  space 
of  smallest  size. 

Considering  the  fact  that  a  mixture  of  oil  and  water 
is  disseminated  through  the  rocks  of  the  earth's  crust,  it  will 
be  evident  that  the  differences  in  surface  tension  will  cause 
a  selective  segregation  of  oil  and  water.  The  water,  be- 
cause of  its  superior  surface  tension,  occupies  the  pores  of 
smaller  diameter;  the  oil  is  driven  into  the  opening  of 
larger  size.  Capillary  pressure  decreases  with  rise  in  tem- 
perature. Because  of  the  increase  in  temperature  due  to 
heat  gradient,  it  is  virtually  negligible  in  rocks  at  a  depth 
"of  several  miles. 


POPULAR  OIL  GEOLOGY.  73 

Conclusions. 

All  the  factors  discussed  separately,  probably  played 
a  part  in  causing  oil  migration.  To  some  extent,  at  least, 
their  effects  can.  be  differentiated.  The  original  sedi- 
ments, which  consist  in  greater  part  of  muds  with  minor 
layers  of  sand  or  perhaps  porous  limestone,  must  suffer 
considerable  compacting  at  the  time  of  their  consolidation 
into  rock.  The  muds  especially  are  subject  to  a  consider- 
able shrinkage  of  volume,  which  is  mainly  the  result  of 
rock  pressure.  The  sands  and  limestones  offer  greater  re- 
sistance to  pressure  and  cannot  be  compacted  to  the  same 
degree.  Their  pores  will  remain  open  and  will  serve  as 
reservoirs  for  the  liquid  materials  squeezed  from  the  clays 
and  mud.  Capillary  pressure  also  plays  a  role  and  prob- 
ably the  most  important  one,  in  affecting  a  primary  con- 
centration of  oil  and  gas  in  the  reservoir  rocks.  Thus  in 
the  progress  of  time,  the  oil  and  gas  contained  in  the  shales 
will  be  driven  out  by  water  because  of  its  greater  capillary 
pressure,  and  will  be  forced  into  the  rock  with  larger  pores 
—the  reservoir. 

Rock  pressure  and  capillary  pressure  are  chiefly  im- 
portant in  collecting  oil  and  gas  in  reservoir  rocks.  They 
will  be  disseminated  through  the  entire  formation,  and  only 
under  very-  exceptional  conditions  can  they  be  concen- 
trated into  commercial  pools  by  rock  pressure  and  capil- 
lary pressure  alone.  Oil  pools  in  fissured  shale  may  owe 
their  existence  mainly  to  such  concentration. 

In  the  majority  of  cases  the  concentration  of  oil  and 
gas  into  commercial  pools  is  the  result  of  the  differences 
in  the  specific  gravities  of  oil,  gas  and  water,  and  of  the 
movement  of  the  underground  water.  Oil  and  gas  rise  to 
the  surface  of  the  water,  and  wherever  currents  exist  move 
ahead  on  the  water  surface  through  the  reservoir  rocks.  A 
concentration  of  large  quantities  of  oil  and  gas  may  take 
place  where  suitable  structural  conditions  exist.  The  term 
"trap"  is  frequently  applied  to  such  a  condition,  and  is 
quite  appropriate. 


74  POPULAR  OIL  GEOLOGY. 

Gas  pressure  and  water  pressure  due  to  head  are  the 
most  important  causes  of  flowing  wells,  with  one  or  the 
other  dominant,  depending  upon  local  conditions. 

Conditioning  Factors  of  Oil  Migration. 

There  are  a  number  of  conditioning  factors  upon 
which  the  movement  of  oil  and  gas  are  dependent.  These 
are  in  part  due  to  the  characteristics  of  the  reservoir,  in 
part  due  to  the  oil,  and  in  part  due  to  local  geological  con- 
ditions. They  are  shown  in  tabulated  form. 

A .  Lithological  character  of  the  reservoir. 

1.  Degree  of  porosity. 

2.  Size  and  continuity  of  pore  space. 

3.  Degree  of  saturation  by  water. 

4.  Proportion  of  induced  to  original  open- 

ings. ^ 

5.  Composition  of  reservoir  as  determining 

relative  adhesion. 

6.  Effectiveness  of  cementation. 

B.  Physical  and  chemical  character  of  oil. 

1.  Gravity. 

2.  Viscosity. 

3.  Proportion  of  gas. 

C.  Geological  factors. 

1.  Structure. 

2.  Character  of  enclosing  beds. 

3.  Local  heat  gradient. 

4.  Composition  of  ground  water. 

5.  Depth  of  burial. 

6.  Geological  history. 

The  characteristics  of  the  reservoir  rock  are  quite  im- 
portant in  determining  the  relative  ease  of  flow.  Ready 
flow  is  favored  by: 

1.  High  effective  porosity. 

2.  Large  and  continuous  openings  or  pores. 

3.  High   proportion   of   induced   openings,   such   as 

fractures,  joints,  solution  fissures. 


POPULAR   OIL  GEOLOGY.  75 

4.  Presence  of  water  under  pressure. 

5.  Cementation  effective  enough  to  hold  and  support 

the  sand  upon  removal  of  oil. 

The  characteristics  of  oil  also  condition  its  movements. 
Ready  flow  is  favored  by : 

1.  High  degree  gravity. 

2.  Low  viscosity. 

3.  High  proportion  of  gas. 

The  greater  the  difference  in  the  specific  gravity  of 
oil  and  water,  the  more  effective  gravitative  separation  will 
be.  The  lower  the  viscosity  of  the  oil,  the  less  the  resist- 
ance that  is  offered  to  movements  through  the  pores  of  rock. 

A  number  of  geological  factors  influence  flow.  Thus, 
steep  dips  favor  flow.  Unconformities  of  the  angular  type 
are  favorable  to  migration  because  of  the  more  rapid  con- 
centration of  oil  from  the  lower  series  into  the  unconform-' 
able  one  above,  due  to  the  greater  ease  of  travel  along  beds 
than  across  them.  Certain  sands  are  so  friable  that  large 
quantities  of  sand  are  ejected  from  the  wells.  Oil  flow  is 
favored  in  these  by  the  presence  of  strong  resistant  enclos- 
ing beds  above  and  below  the  reservoir.  Locally  high  heat 
gradient  has  the  double  effect  of  lowering  the  surface  ten- 
sion and  decreasing  the  viscosity  of  oil.  On  the  whole,  the 
effect  will  be  to  stimulate  circulation.  The  presence  of  sul- 
phated  ground  waters  is  obnoxious  because  it  results  in  the 
production  of  sulphur  compounds  in  the  oil  and  increases 
its  specific  gravity  and  viscosity.  The  latter  two  render 
the  oil  less  mobile.  Depth  of  burial  determines  tempera- 
ture and  pressure  on  the  oil,  the  effect  of  both  of  which  has 
already  been  discussed.  The  past  geological  history  of  an 
oil  field  often  gives  us  an  explanation  of  peculiar  localiza- 
tion of  oil  pools.  Frequent  oscillations  in  elevation  of  a 
district  result  in  changes  in  the  water  level  and  must  of 
necessitv  stimulate  oil  movements. 


POPULAE  OIL  GEOLOGY. 

Laws  of  Oil  Accumulation. 

The  laws  of  oil  accumulation,  although  relatively  sim- 
ple, were  not  clearly  formulated  until  1885.  In  that  year, 
I.  C.  White  published  what  is  known  as  the  "anticlinal 
theory".  This  is  probably  the  most  important  single  con- 
cept of  oil  geology  which,  in  more  or  less  modified  form, 
governs  oil  accumulation  in  virtually  all  oil  fields.  In  oil 
fields  we  do  not  find  the  sedimentary  rocks  flat  and  undis- 
turbed as  they  were  originally  deposited,  but  we  find  them 
folded  and  wrinkled  much  like  the  quilt  on  our  bed  after  a 
night's  sleep.  The  upfolds  or  arches  are  anticlines;  the 
downfolds  or  troughs  are  synclines.  Experience  has 
shown  that  the  higher  parts  of  the  folds,  that  is,  the  anti- 
clines, are  more  likely  to  carry  oil.  This  is  explained  as 
follows : 

The  sandstones  or  limestones  which  act  as  oil  and  gas 
reservoirs  are,  in  most  cases,  saturated  with  water.  They 
are  overlain  and  underlain  by  shale  or  some  other  rock 
which  forms  a  more  or  less  impervious  cover.  Oil  and 
water,  even  if  vigorously  stirred  up  and  shaken  in  a  bottle 
will  not  mix,  but  will  separate  in  two  layers  according  to 
their  weight — the  oil  on  top,  the  water  below.  Similarly 
in  the  oil  sand  such  a  separation  will  take  place.  If  the 
sand  be  completely  saturated  or  filled  with  water,  the  oil 
will  rise  to  the  highest  part  of  the  reservoir — which  is  the 
very  top  or  crest  of  the  anticline.  If  the  sands  are  only 
partially  saturated,  the  oil  will  accumulate  on  top  of  the 
water  level  along  the  sides  of  the  folds.  If  the  sands  are 
dry,  the  oil  of  necessity  will  be  found  in  the  bottom  of  the 
troughs- — or,  to  use  the  geologic  term,  in  the  syncline.  In 
by  far  the  great  majority  of  cases,  the  oil  sands  are  com- 
pletely saturated,  and  the  .oil  accumulates  therefore  in  the 
crests  of  the  anticlines.  These  are  the  conditions  met  with 
in  the  most  fields  of  Wyoming,  California,  and  the  Appa- 
lachians. Whether  or  not  a  sand  is  saturated  can  only  be 
determined  by  drilling. 


POPULAR  OIL  GEOLOGY.  77 

In  many  fields  noticeable  quantities  of  gas  accompany 
the  oil.  This,  being  the  lightest  constituent  present,  rises 
to  the  top  of  the  oil.  The  occurrence  of  gas  wells,  oil  wells, 
and  water  wells  on  the  same  structure  is  explained  by  "the 
fact  that  the  oil  sands  are  penetrated  at  different  eleva- 
tions ;  the  "gas  well  at  the  highest ;  the  oil  well  at  an  inter- 
mediate ;  and  the  water  well  at  a  lower  elevation.  The 
accompanying  figure  makes  this  clear. 


Figure  23.     Section  illustrating  the  occurrence  of  a  gas  well  (A) ; 
an  oil  well  (B),  and  a  water  well  (C)  on  the  same  anticline. 

There  are  a  number  of  other  structural  arrangements 
of  rock  that  afford  suitable  traps  for  oil  accumulation. 
These  will  be  discussed  in  some  detail  in  the  following 
chapter. 

E"o  matter  what  the  structure  may  be,  we  must  have 
a  porous  rock,  usually  a  sandstone,  that  is  capable  of  act- 
ing as  a  reservoir  and  that  is  enclosed  in  relatively  imper- 
vious rock,  usually  shale.  The  arrangement  of  rocks  must 
be  such  that  there  exists  an  opportunity  for  the  accumula- 
tion of  commercial  quantities  of  oil  and  gas.  The  most 
important  single  factor  in  the  locating  of  an  oil  well  is, 
therefore,  the  geologic  structure.  The  chief  value  of  any 
geologist  is  his  ability  to  determine  the  structure  from  the 
distribution  and  arrangement  of  the  rocks  at  the  surface, 
and  to  locate  the  favorable  areas  for  testing.  It  may  be 


78  POPULAR  OIL  GEOLOGY. 

well  to  emphasize  the  fact  that  a  perfect  geologic  structure 
is  not  necessarily  an  assurance  of  a  producing  well.  The 
presence  of  an  oil-pool  can  only  be  determined  by  an  actual 
test.  The  correct  application  of  geologic  principles  does 
not  ensure  success;  it  minimizes  risks.  Under  the  most 
favorable  geological  conditions,  drilling  in  untested  and 
new  areas  has  only  about  one  chance  out  of  three  for  suc- 
cess. On  the  other  hand,  a  disregard  of  geological  condi- 
tions in  drilling  a  well  is  practically  an  assurance  of  fail- 
ure. 

Modifications  of  the  Anticlinal  Theory. 

It  is  to  be  expected  that  this  theory,  since  its  formula- 
tion in  1885,  should  be  subjected  to  considerable  modifica- 
tion. Indeed,  occasionally  it  appeared  to  be  in  actual  vari- 
ance with  observed  facts  and  was  hence  considered  inappli- 
cable. The  growth  of  our  knowledge  of  geology  and  a 
better  and  clearer  understanding  of  the  principles  involved 
in  the  migration  and  in  the  occurrence  of  oil  in  nature  have 
forced  us  to  the  realization  that  the  accumulation  of  oils 
in  various  fields  may  occur  under  different  conditions  and 
that  the  characteristics,  both  geological  and  structural,  of 
oil  pools  may  so  differ  as  to  render  plausible  the  belief  that 
no  single  theory  can  explain  all  accumulations. 

The  fact  that  the  characteristic  features  of  oil  pools 
differ  in  different  fields  is  well  expressed  in  the  following 
words,  ain  any  stated  field,  oil  and  gas  exist  after  certain 
methods  of  'habit'  which  are  found  to  prevail  generally 
throughout  that  field.  This  is  because,  while  the  substances 
adhere  in  their  relations  to  the  structures  present,  there 
are  modifying  conditions  which  cause  certain  peculiarities 
to  run  entirely  through  the  field.  In  a  scientific  study  of 
any  oil  field,  for  the  purpose  of  determining  its  possibili- 
ties, it  is  necessary  to  distinguish  the  features  which  it  has 
in  common  with  other  fields  from  those  in  which  it  differs 
from  them,  and  by  a  process  of  comparison  and  inference 
based  on  detailed  observations  and  calculations,  to  draw 
conclusions  as  to  whether  or  not  the  locality  is  favorable 
for  petroleum". 


POPULAR  OIL  GEOLOGY.  79 

Oil  men  should  realize  the  fact  that  the  accumulation 
of  an  oil  pool  is  the  result  of  a  number  of  more  or  less  com- 
plex features  all  of  which  are  a  function  of  the  general 
geological  and  structural  characteristics  of  a  given  region. 
The  oil  pool  should  not  he  considered  a  geological  entity 
independent  of  the  region  in  which  it  occurs.  The  true  sig- 
nificance of  the  productive  structure  can  be  properly  under- 
stood only  when  we  realize  the  fact  that  it  bears  an  inti- 
mate relationship  to,  and  is  actually  dependent  upon,  the 
geology  and  structure  of  the  entire  surrounding  region. 
Studied  from  such  a  viewpoint,  we  gain  the  proper  per- 
spective and  begin  to  correlate  properly  and  to  appreciate 
the  true  significance  of  observed  facts.  The  geological  and 
structural  features  of  a  pool  in  the  Gulf  Coast  region  of 
Texas  will  not  be  the  same  as  the  characteristics  of  a  pool 
in  Indiana  or  Wyoming  or  California.  The  ability  to  dif- 
ferentiate and  recognize  the  importance  of  these  character- 
istics marks  the  successful  geologist.  A  great  percentage 
of  the  unsuccessful  ventures  in  drilling  prospect  wells  is 
due  to  failure  to  realize  these  differences.  The  oil  man  or 
geologist  may  have  had  a  wide  experience  in  one  field  and 
become  quite  successful  because  the  features  of  the  geology 
and  structure  that  lead  to  the  accumulation  of  oil  in  this 
field  are  clearly  recognized  by  him.  When  confronted  with 
radically  different  geological  conditions  he  has  the  tendency 
to  apply  the  same  familiar  standards  and  judge  accord- 
ingly, in  most  cases  with  fatal  results.  Indeed,  much  of 
the  prejudice  of  the  practical  driller  against  geology  is  due 
to  his  unfortunate  experience  with  some  geologist  who 
failed  to  understand  and  to  apply  correctly  geologic  prin- 
ciples. The  failure  represents  not  the  failure  of  the  science, 
but  the  faulty  and  imperfect  application  by  a  human  being. 
The  principles  of  geology  are  but  tools,  and  the  results  ac- 
complished by  their  use  depend  on  the  ability  and'  genius 
of  the  man  using  them. 


IX.   Maps  and  Their  Uses 

Nearly  every  report  on  an  oil  field,  whether  a  govern- 
ment report  or  one  made  for  private  interests,  includes  a 
map  of  some  sort.  This  is  not  surprising  because  a  great 
amount  of  information  can  be  shown  on  a  map  in  a  con- 
densed form  and  in  such  a  way  as  to  summarize  clearly 
the  important  features  of  the  region.  Three  kinds  of 
maps  are  most  frequently  used.  These  are  topographic 
maps,  geologic  maps,  and' structural  maps. 

Topographic  Maps. 

Topographic  maps  are  intended  to  show  the  configura- 
tion or  relief  of  the  earth's  surface,  the  distribution  of  the 
hills,  valleys,  mountains,  streams,  roads  and  similar  fea- 
tures. The  United  States  Geological  Survey  has  com- 
pleted over  twenty-five  hundred  topographic  maps  scattered 
through  every  state  of  the  union,  each  of  which  covers  an 
area  of  from  about  two  hundred  to  about  three  thousand 
square  miles.  These  maps  show  the  earth's  relief  by  means 
of  contour  lines,  which  are  lines  drawn  through  points  of 
equal  elevation  at  a  definitely  stated  interval,  known  as  the 
contour  interval,  above  sea  level.  On  the  government  maps 
these  contour  lines  are  drawn  in  brown.  Each  fifth  line 
is  drawn  heavy  and  has  inserted  at  frequent  intervals  its 
elevation  above  sea  level.  The  contour  interval  depends  on 
the  ruggedness  of  the  country.  In  the  western  states  it  is 
usually  fifty  feet.  Water  is  always  drawn  in  blue,  while 
the  work  of  man — culture,  as  it  is  called — such  as  roads, 
buildings,  railroads,  and  land  divisions,  is  indicated  in 
black.  The  spacing  of  contours  indicate  the  slope.  A 
long,  gentle  slope  has  few  contours  widely  spaced ;  a  steep 
slope  has  contours  closely  crowded.  The  accompanying 
figure  shows  an  ideal  sketch  of  a  landscape  and  the  corre- 
sponding contour  map. 

The  relief  features  of  the  earth's  surface  are  deter- 
mined by  the  geological  structure.  Much  useful  informa- 

80 


POPULAR   OIL  GEOLOGY. 


81 


tion  can  therefore  be  obtained  from  a  careful  study  of  the 
topography  or  the  topographic  map.  Crystalline  rocks 
are  very  resistant  to  erosion.  They  usually  form  rough, 
irregular,  and  steep  slopes.  The  topography  is  character- 
ized by  general  ruggedness.  Sedimentary  rocks  give  a 
more  varied  topography.  The  well  cemented  sandstones 
and  conglomerates  and  the  limestones  usually  form  the 


Figure  24.     Ideal  landscape  and  its  contour  map. 

(U.  S.  Geol.  Sur.) 

steeper  slopes  and  the  elevations ;  shales  form  the  gentle 
slopes  and  the  valleys.  Horizontal  sedimentary  rocks  pro- 
duce a  decided  similarity  in  surface  features  over  the 
whole  area,  so  much  so  that  almost  any  square  mile  of 
the  area  of  the  map  may  be  substituted  for  any  other  with- 
out producing  any  marked  change.  Occasional  buttes  and 
mesas  may  remain  as  elevations.  The  streams  have  a  char- 
acteristic, treelike  or  dendritic  shape.  Inclined  sedimen- 


82  POPULAR  OIL,  GEOLOGY. 

tary  rocks  produce  a  topography  characterized  by  a  linear 
arrangement  parallel  to  the  strike  of  the  rocks.  The  hard 
layers  form  more  or  less  parallel  hogbacks,  the  softer  lay- 
ers the  valleys  between.  The  main  streams  usually  cross 
hard  and  soft  layers  alike.  The  tributaries  are  confined  to 
the  softer  layers  and  are  arranged  in  a  roughly  parallel 
manner. 

Geologic  Maps. 

The  topographic  map  is  frequently  used  as  a  base  map 
upon  which  is  recorded  by  means  of  suitable  symbols  or 
colors,  the  distribution  of  the  various  geological  formations 
at  the  earth's  surface.  The  structure  of  the  rocks  deter- 
mines this  distribution ;  conversely,  therefore,  the  struc- 
ture may  be  determined  from  the  distribution  of  forma- 
tions as  shown  by  the  map.  Thus  in  dome  folds  we  find 
the  older  rocks  in  the  center  surrounded  by  progressively 
younger  rocks  as  we  go  outward.  In  a  basin  we  find  the 
younger  rocks  in  the  center  surrounded  by  rocks  progress- 
ively older. 

Columnar  Section. 

Every  geological  report  includes  a  columnar  section 
intended  for  the  purpose  of  interpreting  the  map.  This 
is  an  arrangement  of  all  the  formations  in  a  vertical  col- 
umn according  to  age,  with  the  oldest  at  the  bottom.  The 
thickness  of  each  rock  member  and  its  lithologic  charac- 
ter are  also  indicated.  Thus  limestones  are  shown  by 
masonry  pattern ;  sandstones,  by  dots ;  and  shales  by  closely 
crowded  parallel  lines.  Intermediate  rock  types,  such  as 
calcareous  shales,  are  shown  by  a  combination  of  two  such 
patterns.  Certain  beds  of  rock  are  located  with  great  ac- 
curacy in  the  columnar  section  because  they  can  be  readily 
recognized,  and  hence  are  of  value  as  "index  beds"  or  "key 
horizons". 

Structure  Sections. 

Most  maps  are  accompanied  by  a  structure  section. 
This  is  a  drawing  of  a  vertical  section  through  the  earth's 


POPULAR  OIL  GEOLOGY. 


83 


\ 


Figure  25.     Map  and  section  of  ideal  dome. 


84  POPULAR  OIL  GEOLOGY. 

surface  and  shows  the  various  rock  formations  in  their  true 
attitude.  A  structure  section  is  usually  drawn  to  scale, 
consequently  we  can  determine  by  a  direct  measurement 
the  depth  down  to  any  bed  of  -rock  for  any  point  on  the 
line  of  the  section. 

Structure  Map. 

Most  of  the  maps  of  oil  and  gas  fields  are  structure 
maps.  These  show  the  attitude  or  structure  of  a  particular 
bed  of  rock,  such  as  an  oil  sand,  by  means  of  structure 
contours.  These  are  lines  similar  to  the  contour  lines  used 
on  a  topographic  map.  They  are  not,  however,  drawn 
through  points  on  the  earth's  surface — but  instead,  through 
points  of  equal  elevation  on  top  of  a  certain  bed  of  rock. 
The  contours  indicate  by  their  arrangement  the  structure 
of  the  rock  layer  and  its  elevation  above  sea  level  for  all 
points.  Maps  of  this  sort  are  very  useful  as  they  show  at  a 
glance  the  attitude  of  the  rocks  over  the  entire  area  cov- 
ered, and  at  the  same  time  enable  us  to  determine  the 
depth  from  the  earth's  surface  to  any  rock  layer  whose  posi- 
tion is  given  in  the  columnar  section.  The  structure  con- 
tours are  drawn  from  the  surface  exposures  of  the  rock  and 
their  observed  dips  and  strikes,  which  enable  us  to  calcu- 
late the  depth  to  the  rock  in  question.  A  structure  map  can 
be  drawn  with  very  great  accuracy  in  the  developed  fields 
because  reliable  information  can  be  obtained  by  a  study  of 
the  well-logs  and  records. 

Isochore  Lines. 

In  certain  oil  fields  the  beds  of  rock  exposed  at  the 
earth's  surface  are  not  absolutely  parallel  to  the  oil  sand. 
As  a  result  the  normal  distance  between  a  certain  layer  of 
surface  rock  and  the  oil  sand  gradually  diminishes  in  one 
direction.  The  rate  of  approach  for  two  layers  of  rock  is 
subject  to  much  variation.  It  may  be  a  few  feet  per  mile 
or  several  hundred.  This  feature  must  be  considered  in 
interpreting  the  structure  of  any  field,  because  the  struc- 
ture of  the  oil  sand  may  not  coincide  with  the  structure 
of  the  surface  rock.  IIciicc,  I  lie  area  which  appears  to  be 


POPULAR   OIL   GEOLOGY. 


85 


A  Well,  finding  Su  In  .  Shallow  Santf. 
4-  Well,  Of,  In  the  Sh.llo*  Sind. 
1650 Structure  Contour 

Shallow  S«ncf below  TiJetewt. 


#.  Well,  finding  Gu  In  •  Deop  S«nd 
4-W.U.Dqrinth. 

change  in  Intc 
Coil  Bed  and 


Illustration  of  an  anticlinal  gal  field  in  Pennsylvania  in  which  several  sands  are  productive.  A  ihows  lay  and  dip  of  surface  strata,  with.posi- 
tions  of  all  wells;  B  shows  lay  and  dip  of  a  shallow  sand,  with  positions  of  wells  drilled  to  it,  C  is  a  convergence  map  used  in  calculating  the  lay  of  th» 
deep  sand  for  D  ;  O.ihows  lay'and  dip  of  a  deep  land,  with  positions  of  wells  drilled  to  it. 

Figure    26.     The   application   of   convergence   maps. 

(After  Clapp) 


86  POPULAR  OIL  GEOLOGY. 

favorable  as  judged  from  surface  exposures  may  in  reality 
be  unfavorable  in  the  productive  horizon.  For  this  reason 
it  is  necessary  to  determine  the  rate  of  approach  of  a  cer- 
tain keybed  at  the  surface  and  the  oil  sand,  and  to  con- 
struct a  "convergence  sheet",  that  is,  a  map  which  shows 
for  all  points  the  actual  vertical  distance  between  the  key- 
bed  and  the  oil  sand.  This  is  done  by  means  of  isochore 
lines — that  is,  lines  of  equal  distance  which  are  drawn  a 
definite  interval  apart.  The  convergence  sheet — or  iso- 
chore map — can  then  be  superimposed  upon  the  structure 
map  of  the  key  horizon  and  from  the  two,  the  structure 
map  of  the  oil  sand  can  be  drawn. 


X.   Oil  Structures 

Structure. 

Any  arrangement  of  the  rocks  of  such  a  nature  as  to 
form  a  trap  suitable  for  the  accumulation  of  commercial 
quantities  of  oil,  is  known  as  a  "structure".  Such  may 
occur  in  a  great  variety  of  forms  and  in  considerable  com- 
plexity. 

Classification  of  Oil  Fields  on  Basis  of  Structure. 

Experience  has  shown  that  the  various  oil  fields  have 
certain  geological  structures  that  are  characteristic  and  dis- 
tinctive, and  that  vary  decidedly  from  field  to  field.  The 
following  classification  of  American  oil  fields  is  based  on 
structure : 

I.     Fields  with  Folded  Structure. 
The  Appalachian  field. 
Illinois. 

Oklahoma-Kansas. 
North  Texas. 
North  Louisiana. 
California. 
Wyoming. 
Colorado. 

II.     Fields  with  Monoclinal  Dip  (Homoclines). 
Ohio-Indiana. 

California  (minor  importance). 
Wyoming  (minor  importance). 
III.     Fields  on  Domes.  . 
Wyoming. 
Ohio. 

Louisiana-Texas  (Gulf  Coast). 
Mexico. 
IV.     Fields  on  Faults. 

California  (of  minor  importance). 
Wyoming  (of  minor  importance). 
V.     Fields  on  Unconformities. 
California 

Wyoming  (of  very  minor  importance). 
Oklahoma  (Healdton?) 
Quebec  and  Ontario. 
Northern  New  York. 
87 


88 


POPULAR  OIL  GEOLOGY. 


a 

QQ 


POPULAR   OIL  GEOLOGY. 


89 


160  6  ibu    wo  '  560 


x_ 


Figure  28.     The  oil  fields  of  the  United  States. 
(After  Johnson  &  Huntley) 

Fields  with  Folded  Structure. 

By  far  the  greater  part  of  the  oil  fields  of  the  world 
are  in  regions  characterized  by  folding.  This  is  true  of 
virtually  all  important  foreign  fields,  such  as  those  of  Rus- 
sia, Galicia,  Roumania,  India,  Persia,  Peru,  and  the  Dutch 


90 


POPULAR   OIL  GEOLOGY. 


East  Indies.  The  folds  may  consist  of  closely  crowded  and 
rapidly  alternating  anticlines  and  synclines,  or  of  large 
isolated  anticlines  standing  some  distance  away  from  the 
general  area  of  folding.  The  degree  of  folding  differs  very 
decidedly  in  the  different  fields.  Thus,  in  the  Eastern 
fields  and  in  Oklahoma  and  Kansas  the  folds  are  very 
gentle  and  show  dips  of  a  few  degrees  only.  In  some  cases 
the  dips  of  the  beds  are  so  flat  that  they  can  only  be  deter- 


EXPLANATIONS: 

98 Structure-Contour  Lines,  Showing 

•Lay"  of  Gas  Sands. 
Oil  Well;    •&  Gas  Well;    •$- Dry  Hole;        $  Show  of  Gas. 


Figure  29.  Oil  Pool  in  structural  basin,  Oklahoma. 

(After  Clapp) 

mined  with  accuracy  by  means  of  an  instrumental  survey. 
In  the  Wyoming  fields  and  also  in  Colorado  and  Califor- 
nia, the  rocks  show  steeper  dips.  In  Wyoming  dips  of  45° 
are  common.  Vertical  and  even  overturned  dips  occur  in 

California. 

The  oil  and  gas  pools  may  occur  in  all  possible  struc- 
tural relationships  on  the  folds.  The  location  depends  to 
a  large  part  on  the  amount  of  water  present  in  the  reser- 
voir rocks.  In  the  majority  of  cases  these  are  completely 
saturated,  the  oil  and  gas  therefore  occupy  the  crest  of  the 


POPULAR   OIL  GEOLOGY. 


91 


EXPLANATIONS 

•  Oil  Well 

#  Gas  Well 
4-     Dry  Hole 

}-~-  Structure    Contour   Lines,    showing  Elevation 
of  Washington    Coal -Bed  above  Tide 

l^Ji  HJ<   0  1  2  3  f 
Scale  of  Miles 


Figure  30.     Oil  field  on  the  Volcano   Springs  anticline,  W.  Va. 

(After  Clapp) 


92 


POPULAR   OIL  GEOLOGY. 


POPULAR   OIL  GEOLOGY. 


93 


anticline.  This  is  true  of  all  fields  in  Wyoming,  and 
probably  in  Colorado,  and  in  the  greater  number  of  fields 
in  Oklahoma,  Kansas,  and  California.  Partial  saturation 
means  the  location  of  pools  on  the  limbs  of  the  folds  just 
above  the  water  level.  Dry  reservoirs  mean  accumulation 
in  the  bottom  of  the  syncline. 

The  accompanying  maps  show  various  types  of  accu- 
mulation. 

The  larger  anticlines,  which  may  extend  fifty  miles 
or  more,  like  the  Shoshone  anticline  in  the  Wind  River 
Basin  in  Wyoming,  usually  are  not  simple  folds,  but  undu- 
late along  the  crest  or  axis.  Thus  they  have  higher  points 
separated  by  saddles.  The  high  dome-like  bulges  are  called 
"structural  highs,"  the  saddles  are  called  "structural  lows". 
On  the  Shoshone  anticline  there  are  four  well-defined  struc- 
tural highs  which  carry  producing  oil  pools.  These  are 


EXPLANATIONS. 


770 STRUCTURE  CONTOUR  LINES  SHOWINQ 

ELEVATIONS  OF  TOP  OF  BEREA  SAND  ABOVE  TIDE. 
•&  QAS  WELL  WITH  LARQE  PRODUCTION 
#  QAS  WELL  WITH  SMALL  PRODUCTION 
4"  DRY  HOLE   (NO  OIL  OK  QAS) 


Figure  32. 


Gas  on  structural  terrace  in  Ohio. 

(After  Clapp) 


94 


POPULAR  OIL  GEOLOGY. 


known  collectively  as  the  Lander  Oil  Fields.  The  Salt 
Creek  Oil  Field  and  the  Teapot  Dome  in  Wyoming  repre- 
sent structural  highs  on  the  so-called  Salt  Creek  anticline 
which  has  a  north  and  south  extent  of  perhaps  fifty  miles. 

Fields  with  Monoclinal  Dip. 

All  fields  in  which  the  rocks  show  a  general  dip  in 
one  direction  only  will  be  considered  under  this  heading. 
In  general  such  a  structure  is  unfavorable  to  oil  accumu- 
lation. There  are  rare  exceptions  which  may  be  summar- 
ized as  follows: 

Accumulations  as  a  result  of: 

1.  Change  in  rate  of  dip. 

2.  Change  in  direction  of  dip. 

3.  Lenticular  structure. 

4.  Asphalt  sealed  sands. 


EXPLANATIONS. 

.——.2400——  STRUCTURE  CONTOUR  LINES  SHOWING 

DEPTH  OF  CLINTON  SAND  BELOW  SEA-LEVEL. 
4-/WK  HOLE. 
.$.  OA8  WELL. 

•  OIL  WELL 

scJJ^^  one  mil 

Figure  33.   Oil  accumulation 
due  to  change  of  dip.     Ohio. 
(After  Clapp) 


EXPLANATIONS. 

oat snucwRC  COKJOUR  tims  l 

ILCHT/0*  Or  *  JHIH  BID  Of  BLACK  fUHJ  AlOVl  JIDt. 

4  Dtr  HOLE. 
$  e»s  WILL 
•  OIL  meu, 
o H K * i 


Figure  34.  Surface  struc- 
ture on  same  area  as  in  Fig- 
ure 33.  (After  Clapp) 


Structural  Terrace. 

A  change  in  the  rate  of  the  dip  sufficient  to  cause  a 
noticeable  flattening  of  the  rocks  produces  a  structure 
which  is  known  as  a  "structural  terrace"  or  as  an  "arrested 
anticline".  The  change  in  dip  may  be  sufficient  to  retain 


POPULAR  OIL  GEOLOGY. 


95 


oil  and  gas  in  commercial  quantities.  Terraces  of  this  na- 
ture have  been  quite  productive  in  the  Ohio  fields  and  else- 
where, but  have  not  been  tested  out  in  Wyoming  with  the 
possible  exception  of  the  Big  Muddy  field,  which  may  be 
considered  to  be  a  big  terrace.  In  many  cases  an  actual 
trap  for  oil  and  gas  exists,  in  others,  the  oil  is  escaping 
on  the  updip  side  of  the  terrace.  In  the  latter  case  there 
may  be  an  accumulation  because  of  the  slow  motion  of  the 
oil  through  the  terrace  and  the  relatively  rapid  addition 
of  oil  from  the  downdip  side. 


Figure  35.     Oil  accumulation  on  a  structural  ravine.     Ohio. 

(U.  S.  Geol.  Sur.) 

Structural  Ravines  and  Valleys. 

A  change  in  the  direction  of  the  dip  may  produce  a 
sort  of  transverse  wrinkle  in  the  rocks  which  looks  like  a 
valley  or  ravine  on  the  earth's  surface.  Folds  of  this  sort 
are  usually  diagonal  to  the  general  slope  of  the  rocks  and 
die  out  gradually  by  flattening  in  the  direction  of  their 
axes.  They  may  entrap  oil  or  retard  its  passage  for  a 
sufficiently  long  time  to  make  a  commercial  accumulation 
possible.  Many  examples  of  such  structures  are  known 
from  the  Ohio,  Oklahoma  and  Pennsylvania  fields. 


96 


POPULAR   OIL  GEOLOGY. 


Lenticular  Structure. 

In  the  preceding  pages  attention  was  called  to  the  fact 
that  many  sandstones  possess  a  lenticular  structure,  that 
is,  they  disappear  by  thinning  in  various  directions.  A  len- 
ticular sand  of  this  nature  enclosed  in  impervious  beds  and 
not  actually  outcropping  would  form  an  ideal  reservoir  for 
oil  and  gas.  The  gas  sands  of  eastern  Ohio  are  of  this 
nature. 

Asphalt  Sealed  Sands. 

Oil-bearing  sands  that  outcrop  at  the  earth's  surface 
usually  give  oil  and  gas  seeps.  Because  of  this  fact  they 
are  frequently  drilled  down  the  dip  in  the  hope  of  striking 
an  oil  pool.  This  is  not  justified  unless  there  is  evidence 
of  the  existence  of  a  terrace  or  structural  ravine.  Certain 
heavy  oils  may  carry  so  much  base,  especially  in  the  form 


Figure  36.     Accumulations  in  lenticular  sands. 

of  asphalt,  that  this  may  clog  up  all  the  pores  in  the  sand 
in  the  outcrop  and  so  form  an  effective  seal  on  the  remain- 
ing oil.  Such  accumulations  are  reported  from  the  Island 
of  Trinidad.  They  are  very  rare,  however,  and  ne^d  not 
be  expected  in  the  light  Wyoming  and  Colorado  oils,  as 
these  do  not  carry  enough  heavy  base  to  seal  a  sand.  A 
number  of  outcropping  oil  sands  have  been  drilled  down- 
dip,  both  in  Colorado  and  Wyoming,  but  with  disappoint- 
ing results  in  every  case. 

Fields  on  Domes. 

Some  of  the  world's  most  productive  oil  fields  are 
located  on  dome  structures.     Among  the  best  known  of 


POPULAR  OIL  GEOLOGY. 


97 


98 


POPULAR  OIL  GEOLOGY. 


Oil  Structures  in  Wyoming. 


No.  on 
Map         Name 

Produces 

Formation 
at  Surface 

Formation  Producing 
or  Possible  Producer 

1—  Salt  Creek 
2  —  Grass  Creek 
3—  Big  Muddy 
4  —  Elk   Basin 
6  —  Lost  Soldier 
6—  Basin 

7  —  Greybull 
g  —  pilot  Butte 
9  —  Byron 

10—  Little  Buf- 
falo Basin 
11  —  Oregon  Basin 
12  —  Dallas 
13  —  Lander 
14  —  Sage  Creek 
15  —  Thermopolis 
16  —  Douglas 

17  —  Spring  Valley 

Light  Oil 
Light  Oil 
Light  Oil 
Light  Oil 
Light  Oil 
Light  Oil 
and  Gas 
Light  Oil 
Light  Oil 
Light  Oil 
and  Gas 

Gas 
Gas 
Heavy  Oil 
Heavy  Oil 
Heavy  Oil 
Heavy  Oil 
Light  Oil 

Light  Oil 

Niobrara 
Niobrara 
Pierre 
Cody 
Niobrara 

Frontier 
Frontier 
Cody 

Cody  (Niobrara) 

Pierre 
Cody  (Niobrara) 
Chugwater 
Chugwater 
Chugwater 
Chugwater 
White  River 
Tertiary 
Aspen 
Tertiary 

Wall  Creek 
Wall  Creek 
Shannon  and  Wall  Creek 
Wall  Creek 
Wall  Creek 

Mowry 
Mowry  and  Dakota 
Niobrara 

Wall    Creek    and    Dakota 
and  Morrison 
Wall  Creek 
Rusty  Beds,  Cloverly 
Embar  and  Tensleep 
Embar  and  Tensleep 
Embar  and  Tensleep 
Embar  and  Tensleep 
Cretaceous    sands    and 
Basal  White  River. 
Aspen 

19     Verrnillion 

Various 

21  —  Laramie 
Plains 

Pierre 

Frontier 

22     Oil  Mountain 

Sundance 

Embar     Tensleep 

23  —  Rattlesnake 

Various 

Embar     Tensleep 

°4-  •  "Washakic 

25  —  Newcastle 
26  —  Moorcroft 
27  —  Bonanza 

Light  Oil 
Light  Oil 
Light  Oil 

Benton 
Benton  —  Dakota 
Mowry 
Mowry 

Sandstone  in  Benton 
Benton  —  Dakota 
Dakota 
Dakota 

29  —  Cody  or 
Shoshone 

30  —  Shannon 
31     Cotton  wood 

Light  Oil 
and  Gas 
Heavy 
Paraffin 
Oil 

Frontier 

Pierre 
Mowry 

Mowry  —  Thermopolis  — 
Cloverly 

Shannon 
Dakota 

32  —  Cottonwood 

33     Alkali  Butte 

Mowry  and 

34     Dry   Piney 

lower 

Dakota 

35     Rock   Springs 

36     Wheeler 

Pierre 

Wall    Creek 

37  —  Powder 
River  Jet 

Mesaverde 

38"-  Tisdalo 

Sundance 

Morrison 

40  —  Sheep  Mtn. 
41   •  Shell  Creek 



Madison 
Morrison 

Basal  Paleozoic 
Embar     Tensleep 

42-  Dry  Creek 

Cody 

Frontier 

Sundance 

Embar     Tensleep 

44     Manderson 

Cody 

Frontier     Cloverly 

45     Palntrock 

Sundance 

Embar     Tensleep 

Chugwater 

Tensleep 

Madison 

Tensleep 

49  —  Sherard 

Oil  and 
Gas 

Frontier 

Mowry  —  Cloverly 

POPULAK   OIL   GEOLOGY. 

Oil  Structures  in  Wyoming — Cont. 


99 


No.  on 
Map         Name 

Produces 

Formation 
at  Surface 

Formation  Producing 
or  Possible  Producer 

50     Well  Area 

Cody 

Frontier     Cleverly 

51     Tensleep 

Mowry 

52     Bud    Klmball 

Chugwater 

53  —  Mahogany 
Butte 

Madison 

? 

54     Lysite   Mtn 

Mowry 

Cleverly 

55      Black   Mtn 

Mowry 

Cloverly 

56     Lake  Creek 

Frontier 

Mowry     Cloverly 

57  —  Zimmerman 
Butte 

Cody 

Frontier  —  Cloverly 

58  —  Blue  Spring 

Thermopolis 

Cloverly 

59  —  Red  Spring 

Embar 

Tensleep  —  Madison 

60  —  Wildhorse 
Butte 

Chugwater 

Embar  —  Tensleep 

61  —  Lucerne 

Morrison 

Bmbar  —  Tensleep 

62  —  Neiber 

Fort  Union 

Eagle  —  Frontier 

63  —  Sand   Draw 

Cody 

Frontier  —  Cloverly 

64  —  Waugh 

Cody 

Frontier  —  'Cloverly 

6  5  —  TVagonhound 

Cody 

Frontier  —  'Cloverly 

66  —  Enos  Creek 

Cody 

Frontier  —  Cleverly 

67  —  Little  Grass 
Creek 

Cody 

Frontier  —  'Cloverly 

68     Gooseberry 

Cody 

Frontier  —  Cloverly 

69     Fourbear 

Frontier 

Mowry  —  Cloverly 

70  —  Pitchfork 

Mowry 

Mowry  —  Cloverly 

71  —  Spring  Creek 

Mowry 

Mowry  —  Cloverly 

72  —  Frost  Ridge 

Mesaverde 

Frontier 

73  —  Half  Moon 

Frontier 

Mowry  —  Cloverly 

74  —  Teapot 

Pierre 

Frontier 

75  —  North  Lusk 

Morrison 

Embar    (Minnelusa) 

76  —  Coal  Creek 

Mesaverde 

Frontier 

77  —  Poison  Lake 

Casper 

Casper 

78  —  Diamond 

Pierre 

Frontier 

79  .Big  Hollow 

80     Saratoga 

81  —  Muddy  Creek 

Wasatch 

Wasatch 

82  —  Big  Sand 
Draw 

Pierre 

Frontier 

83  —  Rock  Springs 

Fort  Union 

Frontier 

84  —  Dutton 

Chugwater 

Embar  —  Tensleep 

85—  Wallace 
Creek 

Fort  Union 

Eagle  —  Frontier 

8  6  —  Alcova 

Tensleep 

Madison   ? 

87  —  Bates  Hole 

Benton 

Dakota 

88     Goose  Egg 

Chugwater 

Embar—  Tensleep 

89     Iron   Creek 

Frontier 

Dakota 

90  —  Pine  Dome 

Gas 

Sundance 

Embar  —  Tensleep 

Benton 

Dakota 

93     Platte  River 

94     Wheatland 

95     Meridian 

96     Toltec 

97     Medicine  Bow 

98  —  Simpson 
Ridge 

99     Baxter 

100  —  'Castle  Creek 

Pierre 

Frontier 

102     Upton 

Benton 

Dakota 

103  —  South  Lusk 

Tertiary 

? 

104  —  Bitter  Creek 

100 


POPULAR  OIL  GEOLOGY. 


these  are  the  Gulf  Coast  fields  of  Texas,  Louisiana,  and 
Mexico ;  the  Lima  field  of  Ohio ;  and  the  greater  part  of 
the  Wyoming  fields. 

Three  types  of  domes  may  be  recognized.  These  are 
Structural  Domes,  Saline  Domes,  and  Volcanic  Necks. 

Structural  Domes. 

Dome  structures  which  are  the  simple  result  of  fold- 
ing or  arching  of  the  rock  of  the  earth's  crust  are  "Struc- 
tural Domes". 


U.  S.  GEOLOGICAL  SURVEY 


BULLETIN  656    PLATE  IX 
92_ 


STRUCTURE  CONTOUR  MAP  OF  LAMB  ANTICLINE  AND  TORCHLIGHT  DOME  (Nos.  5  AND  6. 

RESPECTIVELY,  ON  PLATE  o  AND  STRATIGRAPHIC  SECTION 

Th«  outcropi  o<  sands  are  mapped  a<  sandr'ones 
By  Ch.,l«  T  Lupton 
.  Scale   «25oo 


Figure  38.     Structure  map  of  Basin  Oil  Fields. 


POPULAR   OIL   GEOLOGY. 


101 


Structure  contours  (lines  of  equal  altitude)  on  top  of 
Greybull  sand.  Numbers  show  distance  above 
sea  level.   Contour  interval.  200  feet 


•  Oil  well 
#Gas  well 
-$-Dry  hole 


Figure  39.     Greybull  Oil  Field. 

(U.  S.  Geol.  Sur.) 

Wyoming,  because  of  its  complex  geological  structure, 
has  a  great  number  of  such  domes.  Most  of  these  are 
really  "structural  highs"  on  well-defined  anticlines.  Be- 
cause of  the  great  interest  in  these  structures  at  the  pres- 
ent time,  they  will  be  discussed  in  some  detail.  Figure  25 
shows  a  structural  section  of  an  ideal  dome  and  also  its 
structural  contour  map.  On  the  map  the  structure  is 
shown  by  contours  one  hundred  feet  apart.  A  number 
of  terms  are  defined  on  the  figure  such  as  major  and  minor 
axes  of  dome,  and  height  of  dome.  The  contours  are 


102  POPULAR  OIL  GEOLOGY. 

O   r.-'-'ir*  A.IO         <r»l.»/M-A'l  Kl .-» 


SECTIONS     CROWING     OCCURRENCE     OF     OIL    AND     GAS     IN 

SOME  OF  THE   ROCKY  MOUNTAIN   FIELDS. 

(Modified   After    Hares.) 

[Correlations   approximate   and    sections    incomplete.        o.,     Oil;     g.,    gas; 
+  ,   seeps  or  small  production  of  oil  or  gas.] 


System 

Spring  Val- 
ley and 
Labarge. 

Big  Horn 
Basin. 

Lander. 

Central 
Wyoming. 

White  River.     + 

Tertiary. 

Wasatch.    -fo. 

Wasatch. 

Wind  River 

Wind  River.     +  ? 

Evanston. 

Fort  Union. 

Absent    or 

Fort  Union. 

Tertiary  (?) 

Lance  or  Ilo. 

Lance. 

Adaville. 

Meeteetse. 

Lewis. 

cd 
B 

• 

4-> 
§ 

Mesaverde, 
or  Gebo 
Eagle. 

Mesaverde 

Mesaverde. 
Teapot.    + 

Parkman. 

% 

Hilliard. 

Cody. 
Pierre 

Mancos 

Steele. 
Shannon,    o. 

02 
§ 

Niobrara. 

5 

Carlile. 

2 

u 

d 
•a 

2 

O 

Frontier,   o. 

Frontier,  o. 
Torchlight. 
Peay    (o.g.) 

Frontier. 

Wall  Creek,     o. 

-     + 

Peay.   + 

u 

Aspen,  o. 

Mo  wry.    o. 

(  +  o.) 

Mowry. 

Thermopo- 
lis.    g. 

Thermopolis. 

Bear  River,   o. 

Cloverly.    g. 
Greybull 

Dakota. 

Dakota.    + 

Lower  Cre- 
taceous (?) 

Lower  Cretaceous 
Shale. 

_    , 

Beckwith. 

(?) 

Morrison,  g. 

Morrison. 

Morrison,    -f- 

Jurassic 

Twin  Creek. 

Sundance 

Sundance. 

Sundance.    + 

Triassic. 

Chugwater 

Chugwater.  +o. 

Chugwater.    + 

Permian. 

Embar   -f 

Embar.    o. 

Embar.   g.  \  — 

Pennsylva- 

Tensleep 

Tensleep.  o. 

Tensleep.     + 

nian. 

Amsden. 

POPULAR   OIL  GEOLOGY. 


103 


SECTIONS   SHOWING    OCCURRENCE    OF    OIL    AND    GAS    IN 

SOME  OF  THE   ROCKY  MOUNTAIN   FIELDS. 

(Modified   After   Hares.) 

[Correlations  approximate  and  sections  incomplete,     o.,   Oil;  g.,   gas; 
+  ,  seeps  or  small  production  of  oil  or  gas.] 


System 

Douglas. 

Black  Hills 

Boulder, 
Colo. 

Florence, 
Colo. 

Tertiary. 

White  River,  o.g 

Fort  Union. 

Tertiary  (?) 

Lance. 

Laramie  (?) 

Fox  Hills. 

Fox  Hills. 

Fox  Hills. 

Trinidad.    ?. 

Montana. 

Pierre. 
Parkman  (?) 

Shannon  ?  + 

Pierre.    + 

Pierre. 
Hygiene, 
o.g. 

(0.) 

Pierre, 
(o.) 

m 

0 

Niobrara 

o 
• 

Benton.   +o.g. 

Carlile.    -4- 

Benton.  o.? 

Carlile.    + 

<D 
h 

u 

d 
-o 

Wall  Creek  ? 

Greenhorn. 

Greenhorn. 

Colora 

Mowry. 
(o.?) 

Graneros. 
Mowry.   o. 

_ 

Graneros. 

"Cloverly." 
o  -4- 

Dakota.   + 

Dakota.    + 

'Dakota"    -f 

Fuson.   + 

Lakota. 

Cretaceous 
(?) 

Morrison. 

Morrison. 

Morrison. 

Morrison.    -f 

Jurassic 

Sundance. 

Sundance. 

Triassic. 

Chugwater. 

Spearfish. 

. 

Minnekahta. 

Lykins. 

Forelle  (?). 

Opeche. 



Satanka   ?   + 

Minnelusa.   o. 

nian. 

Casper.  + 

Pahasapa.    + 

Englewood. 

104 


POPULAR   OIL   GEOLOGY. 


SECTIONS   SHOWING    OCCURRENCE    OF    OIL    AND    GAS    IN 

SOME  OF  THE   ROCKY  MOUNTAIN   FIELDS. 

(Modified   After   Hares.) 

[Correlations  approximate  and  sections  incomplete,     o.,   Oil;  g.,   gas; 
+  ,  seeps  or  small  production  of  oil  or  gas.] 


System 

Western    Colo. 

San    Juan, 
Utah. 

Grand   Co.,   Utah. 

Green  River     + 

Green  River,     -f 

Tertiary. 

Wasatch   o.g. 

Wasatch.    + 

Tertiary  (?) 

Mesaverde.    o.g. 

Mesaverde. 

Cretaceous. 
Colorado.  Montana. 

Mancos.     + 

Mancos.    -f 

Dakota.    + 

Dakota. 

Cretaceous 
(?) 

Flaming  Gorge 

McElmo.    + 

Jurassic 

White  Cliff. 

La  Plata. 

La  Plata. 

Triassic. 

Dolores. 

Pecos  Valley,  N.  M. 

Permian. 

Moencopie. 

Red  Beds. 

Pennsylva- 
nian. 

Goodridge.    o. 

Delaware,    o.g. 

POPULAB  OIL  GEOLOGY.  105 

closely  crowded  on  one  side,  indicating  a  steep  slope  as  is 
well  brought  out  in  the  section. 

Wyoming. 

The  accompanying  sketch  map  of  Wyoming  shows  the 
location  of  a  number  of  structures  through  the  state.  The 
accompanying  table  summarizes  such  data  as  is  available 
for  a  number  of  these.  The  rock  formation  at  the  surface 
and  the  possible  oil  horizons  are  indicated.  In  order  to 
understand  the  table  there  is  given  a  columnar  sec- 
tion of  the  geologic  formation  of  the  Rocky  Mountains. 
Oil  and  gas  have  been  produced  in  commercial  quantities 
only  from  the  Cretaceous  .  and  the  Carboniferous  rocks. 
The  most  important  production  comes  from  the  Wall  Creek 
sandstone  of  the  Frontier  formation,  followed  in  order  by 
the  Shannon  sandstone  of  the  Pierre  formation,  by  a  sand 
in  the  Mowry  shale,  the  Rusty  Beds  in  the  Thermopolis 
shale,  the  Greybull  sand  in  the  Dakota,  and  possibly  a 
stray  sand  near  the  base  of  the  Niobrara.  Gas  under 
heavy  pressure  occurs  in  the  Morrison  formation.  The 
oil  from  the  Cretaceous  rocks  is  a  very  high  grade  light 
paraffin  base  oil.  The  Carboniferous  oil  comes  from  the 
Embar  and  the  Tensleep  sandstones,  and  is  a  heavy  black 
asphalt  base  oil  of  minor  importance. 

Of  the  Wyoming  fields  the  most  important  producers 
are :  Salt  Creek,  Grass  Creek,  Big  Muddy,  Lance  Creek, 
Rock  River,  Elk  Basin,  Lander,  Greybull,  Basin,  Pilot 
Butte,  Lost  Soldier,  Douglas,  and  Byron.  Wells  of  com- 
mercial capacity  are  reported  from  many  other  fields,  in- 
cluding Thermopolis,  Big  Hollow,  Notches,  Osage,  and 
Sherard.  Gas  has  been  encountered  in  large  quantities  in 
Oregon  Basin,  Little  Buffalo  Basin,  Hidden  Dome,  near 
Worland,  Pine  Dome,  Big  Sand  Draw,  and  Garland. 
Sketch  maps  of  several  of  the  more  prominent  fields  are 
given.  * 

Colorado. 

The  Colorado  fields  are  in  part  located  in  regions  of 
folded  rocks,  in  part  on  monoclines,  and  in  part  on  simple 
domes.  Colorado  is  the  oldest  producing  oil  state  in  the 


106 


POPULAR  OIL  GEOLOGY. 


.-If 

mm  111 1 


POPULAR  OIL  GEOLOGY.  107 

Rockies.  The  first  oil  was  produced  in  1862  in  the  Flor- 
ence District  from  an  oil  spring,  since  which  time  a  small 
production  has  been  maintained.  The  first  well  was  drilled 
in  18  76.  This  field  is  unusual  in  that  the  accumulation 
takes  place  in  fissured  shales  and  in  open  joints  and  is 
apparently  independent  of  folding.  The  production  of  this 
district  is  declining  rapidly. 

The  Boulder  District  was  the  scene  of  great  excite- 
ment a  few  years  ago.  The  production  has  always  been 
small  and  has  never  exceeded  one  hundred  thousand  bar- 
rels in  any  one  year.  The  accumulation  here  has  taken 
place  in  a  plunging  anticline.  The  field  is  practically 
exhausted. 

De  Beque  and  Rangely. 

A  number  of  wells  have  been  drilled  near  De  Beque 
and  Rangely  in  the  northwestern  part  of  the  state.  These 
have  been  unsuccessful  although  a  small  production  of  high 
grade  oil  could  undoubtedly  have  been  secured  had  it  been 
desired.  No  attempt  to  secure  this  was  made  at  that  time 
because  of  the  low  value  of  crude  oil.  These  wells  ob- 
tained small  flows  of  oil  or  gas  in  the  basal  part  of  the 
White  River  formation,  the  top  of  the  Wasatch,  the  top 
of  the  Mesaverde,  from  sands  in  the  Mancos  shale,  and 
from  the  Dakota  sandstone.  Favorable  structures  in 
these  formations  merit  careful  investigation,  and,  other 
geological  conditions  being  favorable,  promise  to  yield 
small  capacity  wells  of  high  grade  oil. 

Eastern  and  Southeastern  Colorado. 

The  foothills  region  is  in  general  rather  unfavorable 
to  oil  accumulation  because  of  the  absence  of  minor  folds 
parallel  to  the  main  uplift  of  the  Front  Range.  "No  large 
producing  fields  need  be  expected  here,  although  small 
fields  located  structurally  like  Boulder  and  Florence  may 
be  discovered. 

The  Plains  region  is  for  the  greater  part  of  its  area 
unfavorable  because  the  Pierre  shale,  which  with  the  un- 
derlying and  interbedded  sands  is  the  most  promising  oil 
carrier,  lies  so  deep  as  to  be  out  of  reach  of  the  drills,  or 


108 


POPULAR   OIL   GEOLOGY, 


1|.:|!      : 

-4  H-M 

• 
1         :  I        ^    : 

i  ^fc 

; 

E 

1 

i      & 

r-1  •: 

i  ~i      F"-  h 

:t^C 

1 

n 

'       :U~-I:    :|    : 

L_._L     J 

i      :          •    f*. 

:        :   AN* 

S 


L. 


S 


r-1-g 

:     hs 

•  _« 


i — 


POPULAR  OIL  GEOLOGY.  109 

is  covered  by  unconformable  Tertiary  formations  which 
completely  mask  the  structure  of  the  underlying  rocks. 

Much  interest  has  been  aroused  in  the  southeastern 
part  of  the  state,  especially  in  Kiowa,  Otero,  Baca,  Las 
Animas,  Bent,  Pueblo,  and  Cheyenne  Counties.  These 
undoubtedly  deserve  careful  investigation,  especially  as 
these  Counties  contain  good  structures.  In  this  part  of 
the  state  as  well  as  elsewhere,  the  Cretaceous  formations 
are  undoubtedly  the  most  promising  and  should  receive 
the  most  attention.  The  nearness  to  the  Oklahoma  line 
is  frequently  cited  as  proof  of  the  likelihood  and  even  the 
certainty  of  the  existence  of  large  oil  pools.  As  a  mat- 
ter of  fact  the  northwestern  part  of  Oklahoma  does  not 
contain  any  important  oil  or  gas  fields.  All  of  these  are 
restricted  to  the  eastern  half  of  the  state.  A  number  of 
wells  have  been  drilled  in  the  western  half  of  Oklahoma 
without  success.  The  geological  formations  in  this  part 
are  also  distinctly  unfavorable  to  oil.  For  these  reasons 
the  State  Geologist  of  Oklahoma  concludes  that  "the  pros- 
pects for  future  development  in  this  general  region  (north- 
western Oklahoma),  as  evidenced  by  formational  charac- 
teristics and  by  past  drilling  records,  are  not  of  the 
brightest."  We  may  safely  conclude,  therefore,  that  the 
Carboniferous  sands  are  no  more  promising  in  southeastern 
Colorado  than  in  northwestern  Oklahoma.  Any  attempts 
to  drill  for  these  Carboniferous  sands  should  only  be  under- 
taken by  those  abundantly  able  to  bear  the  financial  burden 
and  with  the  full  knowledge  that  the  chances  for  success  are 
less  promising  than  could  be  desired. 

On  the  whole  Colorado  is  less  favorably  situated  with 
respect  to  oil  than  Wyoming.  The  section  of  the  Creta- 
ceous rocks  is  not  as  favorable  because  of  the  virtual  ab- 
sence of  sands  capable  of  acting  as  reservoirs.  In  addition, 
the  structure  of  the  Cretaceous  rocks  is  relatively  simple, 
consequently  the  possibilities  of  structural  arrangements 
favorable  to  oil  accumulation  are  far  less  than  in  Wyoming 
where  the  geological  structure  of  the  Cretaceous  rocks  is 
much  more  complex.  Large  fields  need  not  be  expected  in 
Colorado.  The  possibilities  are  bright  of  finding  a  few 


110 


POPULAR   OIL  GEOLOGY. 


Figure  42.     Section  of  saline  dome. 

(After  Hager) 

scattered  fields  with  wells  of  small  capacity  that  yield  a 
high  grade  oil. 

New  Mexico. 

There  has  been  a  great  deal  of  interest  in  the  oil  pos- 
sibilities of  New  Mexico  during  the  past  year  (1919),  and 
a  great  deal  of  exploratory  work  has  been  undertaken  in 
this  State.  This  is  due  to  the  stimulating  high  prices  for 
crude  oil  and  its  products  as  well  as  the  phenomenal  devel- 
opment of  the  North  Texas  oil  fields  around  Ranger,  Burk- 
burnett  and  Wichita  Falls.  Wildcat  wells  are  being  drilled 
at  the  present  moment  in  various  parts  of  the  Pecos  Valley, 
in  the  Tularosa  basin,  in  the  San  Juan  region,  near  Albu- 
querque, near  Magdalena,  near  Columbus,  etc.  Small  pro- 
duction of  heavy  oil  is  reported  from  the  Seven  Lakes  dis- 
trict, northeast  of  Gallup  and  from  the  southern  part  of 
the  Pecos  Valley  near  Artesia. 

Pecos  Valley. 

The  greatest  activity  is  in  the  Pecos  Valley,  which  is 
located  in  the  eastern  part  of  the  State,  to  the  east  of  the 
front  ranges  of  the  Rockies.  This  district  is,  therefore,  a 
transition  from  the  Plains  region  with  its  nearly  horizontal 
rocks,  to  the  Rocky  Mountains,  characterized  by  decided 
well  developed  folding.  The  Pecos  Valley  and  the  adja- 
cent part  of  the  Pan  Handle  of  Texas  is  characterized  by 


POPULAR  OIL  GEOLOGY.  Ill 

flat  dips  generally  easterly,  broken  by  a  great  number  of 
very  gentle  folds.  The  geological  conditions  and  the  struc- 
ture here  are  in  many  respects  similar  to  those  in  the  Mid- 
Continent  oil  fields,  of  which  this  area  may  be  considered 
to  be  a  possible  westward  extension.  The  surface  forma- 
tions are  usually  red  beds  of  Triassic  to  Permian  age.  The 
topography  shows  a  decided  tendency  to  conform  to  the 
structure.  Production  is  expected  in  the  Pennsylvanian 
and  possibly  Mississippi  an  formations.  Huge  gas  flows 
have  been  encountered  in  wells  drilled  at  Amarillo,  Texas, 
one  of  which  is  reported  to  have  the  largest  capacity  of  any 
gas  well  in  the  Mid-Continent  field.  Small  flows  of  oil  are 
reported  from  wells  near  Artesia  and  Roswell.  Encourag- 
ing shows  of  oil  and  gas  are  reported  from  Tucumcari. 
Several  wells  drilled  on  the  Anton  Chico  Grant,  northwest 
of  Santa  Rosa,  were  somewhat  disconcerting.  These  were 
drilled  into  granite  and  failed  to  encounter  the  Carbonifer- 
ous formations  in  which  production  was  expected.  As  is 
naturally  to  be  expected,  a  great  deal  of  the  drilling  is  done 
ill-advisedly  and  consequently  with  very  slight  chance  of 
success.  On  the  whole,  however,  enough  work  has  been 
done  to  prove  the  generally  petroliferous  character  of  the 
Carboniferous  formations.  One  discouraging  feature  is 
the  scarcity  of  capable  reservoir  rocks  in  them.  Wherever 
these  are  present,  a  proper  structure  is  sufficiently  promis- 
ing to  warrant  drilling. 

San  Juan  Basin. 

The  San  Juan  Basin  is  located  in  the  northwestern 
part  of  the  State.  The  greater  part  of  this  basin  lies  in 
the  adjacent  portions  of  Utah  and  Colorado.  The  basin 
itself  'is  a  synclinal  depression  practically  surrounded  by 
-towering  mountain  ranges.  From  the  standpoint  of  struc- 
ture and  geology  this  district  is  a  part  of  the  Rocky  Moun- 
tain oil  fields.  The  formation  of  interest  as  a  possible  oil 
producer,  is  the  Cretaceous.  This  is  in  some  respects  simi- 
lar to  the  Cretaceous  farther  north  in  Colorado  and  Wyo- 
ming. It  differs  in  that  the  marine  shales  (known  as  the 


112 


POPULAR   OIL   GEOLOGY. 


Mancos)  are  very  much  thinner  and  seem  to  lack  capable 
reservoir  sands.  The  upper  part  of  the  Cretaceous  (the 
Mesaverde  formation)  comprises  a  thick  series  of  alternat- 
ing sandstones  and  shales  and  thick  coal  beds.  The  sand- 
stones are  the  dominant  members  of  this  series  and  are  so 
abundant  as  to  hinder  an  effective  concentration  of  oil. 
Shows  and  seeps  of  oil  in  these  sands  are  quite  common 
throughout  the  entire  area.  It  is  very  improbable  that 
large  production  will  ever  be  encountered  in  this  formation, 
but  the  chances  of  getting  small  wells  on  pronounced  struc- 
tures in  this  general  area  must  be  considered  promising. 
A  number  of  wells  yielding  small  production  have  been 
brought  in  in  Utah  and  several  in  the  Seven  Lakes  district 
in  New  Mexico.  The  whole  area  is  seriously  handicapped 
by  the  absence  of  railway  connections  and  it  is  unlikely 
that  any  development  here  can  be  profitable  under  present 
conditions  because  of  transportation  difficulties,  the  general 
high  cost  of  operation,  and  the  small  production  met  with 
to  date. 

Lima,  Ohio. 

The  Lima  field  of  Ohio  is  located 
that  extends  over  the  entire  state  and 
the   Cincinnati  anticline.      The  dips 
gentle  as  to  be  unapparent  to  the  eye. 
stone  of  the  Ordovician  age  is  the  oil 
erly  was  a  very  important  producer, 
of  such   large  extent   are   frequently 


on  a  huge  dome  fold 
which  is  known  as 
of  the  fold  are  so 
The  Trenton  lime- 
reservoir  and  form- 
Folds  as  broad  and 
called  go-anticline. 


Figure  43.     Idealized  section  of  Mexican  oil  structure  of 
volcanic  neck  type. 

(After  Clapp) 


POPULAK  OIL  GEOLOGY. 


113 


Saline  Domes. 

The  oil  fields  of  the  Gulf  Coast  of  Texas  and 
Louisiana  are  characterized  by  deposits  of  salt  and  by  salt 
springs.  They  are  usually  of  rather  limited  extent,  and 
appear  occasionally  as  slight  elevations  above  the  plains. 
The  first  of  these  domes  discovered,  was  the  Spindle  Top 
field  at  Beaumont.  This  covered  a  surface  area  of  only 
three  hundred  acres  but  produced  the  largest  gusher  of  the 
United  States — known  as  the  Lucas  well — which  had  an 
initial  capacity  of  seventy-five  thousand  barrels  per  day. 

The  salt  usually  occurs  in  the  center  of  the  dome 
and  at  a  considerable  distance  under  the  surface.  There 
is  a  tendency  for  the  saline  domes  to  be  arranged  in  two 
sets  in  parallel  straight  lines  intersecting  at  nearly  ninety 
degrees.  This  has  led  geologists  to  the  belief  that  the 
domes  are  located  at  the  intersection  of  major  faults  or 
lines  of  weaknesses  along  which  the  circulation  of  under- 
ground water  is  stimulated.  At  the  intersection  of  two 
such  faults,  salt  is  crystallized  out,  making  room  for  itself 
by  bowing  up  the  overlying  rocks  and  producing  the  dome. 

Others  have  explained  the  domes  as  the  result  of 
the  deposition  of  salt  around  mineral  springs  simultan- 
eously with  the  deposition  of  the  enclosing  sediments  on 
the  ocean  bottom.  After  elevation  the  sediments  were 
compacted  and  settled  down  around  the  core  of  salt  and 
thus  produced  the  dome. 


Figure  44.     Section  through  Mexican  oil  field. 

(After  Johnson  and  Huntley) 


114  POPULAR  OIL  GEOLOGY. 

Volcanic  Domes. 

The  most  productive  wells  in  the  world  occur  in, 
Mexico  in  fields  that  owe  their  presence  to  intrusion  of 
igneous  rocks  as  necks  or  plugs.  The  igneous  rock  in 
forcing  its  way  through  the  practically  horizontal  sedi- 
ments has  arched  them  slightly,  has  fractured  and  shat- 
tered them,  and  thus  has  produced  both  a  reservoir  and  a 
suitable  structure. 

The  structure  resembles  to  some  extent  a  funnel.  This 
is  the  result  of  arching  or  bowing  up  of  the  sediments  all 
around  and  for  some  distance  away  from  the  igneous  rock 
at  the  time  of  intrusion,  followed  by  a  dragging  downward 
of  the  edges  of  the  sediments  at  the  very  contact  due  to 
shrinkage  of  igneous  rock  on  cooling.  A  characteristic 
volcanic  dome  is  shown  in  Figure  43.  The  volcanic 
domes  similar  to  the  Saline  domes  are  apparently  localized 
in  intersecting  straight  lines  which  represent  lines  of 
weakness  in  the  earth's  crust. 


Figure  45.     Oil  pool  sealed  in  by  fault. 

Fields  on  Faults. 

Faults  have  in  some  instances  exerted  a  beneficial 
effect  in  bringing  about  a  concentration  of  oil.  This  is 
due  to  the  fact  that  they  carry  finely  ground  up  rock  of 
claylike  appearance  known  as  gouge,  which  is  impervious 
to  water  circulation,  and  hence  may  serve  as  a  seal  on  an' 
oil  sand.  Large  production  has  been  obtained  under  such 
conditions  in  the  Los  Angeles  field  in  California  as  well 
as  elsewhere. 


POPULAR  OIL  GEOLOGY. 


115 


In  southwestern  Wyoming  a  huge  north  and  south 
fault  exists  known  as  the  Absaroka  fault,  along  which  there 
are  a  number  of  oil  springs  and  seeps.  A  small  production 
has  been  obtained  from  sands  sealed  by  minor  faults  in 
the  Douglas  field  of  Wyoming. 

In  the  case  of  faulted  strata,  only  one  side  affords 
the  right  conditions  for  accumulation.  This  depends  on 
the  inclination  of  the  fault  plane  and  the  strata.  The 
accompanying  figure  indicates  why  on  one  side  of  the 
fault  we  obtain  a  water  well,  on  the  opposite  side,  gas. 
or  oil. 

Fields  on  Unconformities. 

The  gas  fields  of  northern  New  York  which  are 
located  in  the  Potsdam  sandstone,  occur  at  an  uncon- 


Figure  46.     Gas  pool  at  unconformity.     New  York. 

(After  Clapp) 

formity  below  this  formation.  The  gas  is  concentrated  in 
commercial  pools  on  the  top  of  the  old  hills  left  in  the 
older  erosion  surface  below  the  unconformity  (see  figure 
46).  In  a  similar  manner  commercial  gas  accumulations 
occur  in  Quebec  and  northern  Ontario. 

Small  oil  pools  in  the  Brenning  Basin  near  Douglas, 
Wyoming,  owe  their  existence  to  an  unconformity.  Here 
the  oil  bearing  Cretaceous  rocks  have  a  homoclinal  struc- 
ture with  northeasterly  dips  of  about  20°  to  24°.  Tertiary 
rocks  have  been  deposited  across  their  beveled  edges.  The 
Tertiary  clays  are  impervious  enough  in  some  cases  to 
seal  the  underlying  Cretaceous  sands,  and^so  cause  a  small 
accumulation.  It  will  be  evident,  however,  that  by  far  the 
greater  part  of  the  oil  originally  present  in  the  Cretaceous 


116 


POPULAR  OIL  GEOLOGY. 


rocks  in  this  field  must  have  been  dissipated  at  the  earth's 
surface  during  the  time  that  these  rocks  were  tilted  and 
eroded  down  to  the  flat  surface  on  which  the  younger 
Tertiaries  rest.  All  wells  in  this  field  are  of  very  limited 
capacity  and  short  life. 


Figure  47.     Oil  pool  on  an  unconformity.    Wyoming. 


Summary. 

By  far  the  great  majority  of  oil  fields  occur  on  folded 
rocks.  Anticlines  and  domes  are  the  most  favorable  struc- 
tures and  should  be  the  first  to  receive  attention.  In 
regions  of  monoclinal  dip,  that  is,  wherever  the  strata  are 
inclined  in  one  direction  only,  accumulation  may  take 
place  on  a  structural  terrace  or  structural  ravine,  or  per- 
haps in  a  lenticular  sand.  Wherever  igneous  rock  has 
been  intruded  in  the  shape  of  volcanic  necks  or  plugs,  there 
may  have  been  sufficient  structural  disturbance  to  cause 
favorable  conditions  for  oil  accumulation.  This  is  true 
only  under  exceptional  conditions.  The  same  holds  for 
faults  Which  may  serve  to  seal  in  small  oil  or  gas  pools. 
Most  eccentric  of  all  accumulation  and  probably  the  least 
reliable,  are  the  gas  and  oil  pools  on  unconformities. 

In  the  majority  of  oil  fields,  pools  may  be  expected 
to  occur  in  a  number  of  these  structures.  Every  type  of 
accumulation  is  known  in  California  with  the  exception  of 
that  around  volcanic  necks.  In  Oklahoma,  pools  are  lo- 
cated on  anticlines,  domes,  structural  terraces,  and  lenticu- 
lar sands.  Certain  of  the  oil-bearing  sands  of  Pennsyl- 
vania, Kentucky,  and  Oklahoma  are  dry.  Oil  pools  are, 
therefore,  localized  in  the  synclines  and  basins  in  some  of 
the  pools  in  these  fields. 


XL   Popular  Fallacies  in  Oil  Geology 

Not  all  Rocks  Carry  Oil. 

One  of  the  erroneous  statements  frequently  made  is 
that  aall  rocks  carry  oil" ;  consequently,  that  all  that  is 
necessary  to  warrant  drilling  is  a  favorable  geologic  struc- 
ture. This  is  by  no  means  true.  The  crystalline  rocks 
are  nowhere  producing  commercial  quantities  of  either 
oil  or  gas.  As  a  matter  of  fact  there  is  no  probability  of 
ever  obtaining  a  production  except  from  the  sedimentary 
rocks.  Neither  do  all  sedimentary  rocks  carry  oil  and  gas. 
The  rocks  deposited  in  deserts  or  by  mountain  torrents 
are  formed  -under  such  conditions  that  life  forms  cannot 
flourish.  Consequently  they  do  not  contain  the  raw  ma- 
terials necessary  for  the  production  of  oil  or  gas.  The 
marine  sediments,  especially  those  deposited  near  the 
shore,  are  the  most  favorable  because  here  life  of  all  kinds 
is  abundant.  As  a  matter  of  fact  probably  every  marine 
rock  analyzed  with  sufficient  care  will  yield  at  least  a  trace 
of  oil.  Such  sedimentary  rocks  are  usually  dull  colored — 
gray,  black,  brown,  or  dark  green.  The  bright  colored 
sediments,  especially  the  bright  red  ones,  are  distinctly 
unfavorable  as  oil  producers.  There  is  no  reason,  however, 
for  condemning  marine  sediments  above  or  below  red 
beds.  These  may  be  productive,  as  are  the  Embar  and 
Tensleep  formations  below  the  Chugwater  Red  Beds  of 
Wyoming. 

Again  it  is  well  to  realize  the  fact  that  commercial 
production  can  be  expected  only  where  suitable  reservoirs 
and  enclosing  beds  exist.  We  must  have  sands  or  sand- 
stones open  in  part,  or  perhaps  porous  limestones,  imbedded 
in  shales  or  other  impervious  rock.  In  the  case  of  pro- 
ducing fields,  shales  are  usually  three  or  more  times  as 
thick  as  the  sands.  In  Wyoming,  the  shales  are>  from  six 
to  ten  times  as  thick  as  the  sandstones.  A  series  of  marine 
rocks,  essentially  sands,  is  so  porous  that  oil  and  gas  are 
disseminated  in  small  quantities  throughout  the  whole 

117 


118  POPULAR  OIL  GEOLOGY. 

formation  and  are  not  concentrated  sufficiently  to  be  of 
value.  A  number  of  sands  may  occur,  all  of  which  appear 
to  be  favorable  for  oil  production  in  a  certain  field.  Never- 
theless, only  one  or  two  of  these  may  afford  commercial 
pools.  The  results  of  a  thorough  test  are  the  most  valuable 
guide  in  determining  the  oil  possibilities  of  the  sand  in 
other  structures  in  the  same  field,  and  should  be  carefully 
considered  in  making  future  locations. 

Drill  Deep. 

Very  frequently  the  statement  is  made  that  all  that  is 
necessary  to  ^  secure  oil  is  to  drill  deep  enough,  and  the 
failure  to  obtain  oil  in  a  well  is  explained  as  lack  of  depth. 
This  is  possibly  true  in  the  case  of  an  individual  well  cor- 
rectly located  on  a  structure,  but  as  generally  applied,  the 
statement  is  fallacious.  To  drill  without  the  knowledge 
that  the  well  is  actually  on  a  favorable  structure  and  that 
in  depth  we  may  hope  to  strike  a  favorable  reservoir,  is  a 
waste  of  money  and  time.  Whenever  this  argument  is 
presented  it  is  well  to  call  to  mind  the  fact  that  if  depth 
were  the  only  requisite  to  a  producing  well,  the  investor 
would  probably  prefer  to  sink  wells  in  his  own  back  yard, 
where  markets  and  transportation  facilities  are  at  hand. 

"Favorable  Indications." 

'A  great  many  popular  misconceptions  center  about 
the  so-called  "favorable  indications".  Among  these  we 
may  include  the  following : 

1.  Oil  and  gas  seeps  at  the  surface. 

2.  The  presence  of  salt  water. 

3.  The  presence  of  oil  residue  in  rocks  at  the 

surface. 

4.  The  presence  of  "oil  shale". 

5.  Traces  of  gas  and  oil  in  wells. 

Seeps. 

Wherever  oil  and  gas  escape  from  rocks  at  the  earth's 
surface  we  have  a  "seep".  The  Quantities  that  escape 
may  be,  and  usually  are,  very  slight.  The  presence  of 


POPULAR  OIL  GEOLOGY. 


119 


such  seeps  is  frequently  cited  as  a  proof  of  the  existence  of 
oil  pools  under  the  surface.  This  is  not  necessarily  their 
true  significance.  They  only  prove  that  the  formation  does 
carry  oil,  and  that  it  would  be  worth  drilling  provided  a 
suitable  structure  could  be  found.  Only  from  this  stand- 
point are  oil  seeps  "favorable  indications".  Seeps  are  most 
common  along  the  outcrops  of  the  reservoir  rocks.  This 
rock,  therefore,  could  tnot  be  considered  a  possible  pro- 
ducer at  the  point  of  the  seep.  Some  distance  away,  how- 
ever, there  may  be  an  anticline  or  dome  which  carries  this 
reservoir  rock  at  a  drillable  distance  under  the  surface. 
Under  such  conditions,  the  fact  that  a  seep  is  known  to 


Figure  48.     Oil  seeps  and  accumulation  down  dip. 


exist  some  distance  away  in  the  outcrop,  is  an  encouraging 
feature.  Seeps  occur  under  a  great  variety  of  conditions. 
In  very  many  cases  these  are  such  as  to  preclude  all  prob- 
ability of  the  presence  of  commercial  pools.  A  seep  may 
then  indicate  that  the  oil  is  being  dissipated  and  not  being 
retained.  Seeps  are  only  of  value  as  proving  the  petrolif- 
erous character  of  a  formation.  In  themselves  they  are  no 
justification  whatever  for  drilling  a  well  or  locating  an  oil 
claim. 

Salt  Water. 

The  salt  water  so  commonly  met  with  in  oil  wells  rep- 
resents the  ocean  water  which  was  originally  included  in, 
the  pores  and  openings  in  the  sediments  at  the  time  of  their 
deposition  on  the  ocean  floor.  Water  so  occluded  and  re- 
tained is  also  known  as  connate  water. 

The  frequent  association  of  brine  with  oil  has  led  to 
the  popular  belief  that  salt  water  invariably  indicates  the 


120  POPULAR  OIL  GEOLOGY. 

presence  of  oil.  This  is  by  no  means  true.  Brines  may  or 
may  not  be  accompanied  by  oil.  The  presence  of  salt  water 
is,  therefore,  of  no  particular  diagnostic  value. 

Residual  Deposits. 

Asphalt  or  paraffin  in  the  surface  outcrop  of  rocks 
has  practically  the  same  significance  as  have  oil  and  gas 
seeps.  They  prove  that  the  formations  are  petroliferous, 
but  do  not  indicate  that  an  oil  pool  is  located  beneath  them. 
Drilling  down  dip  from  the  outcrop  in  such  rocks  has  only 
a  bare  chance  for  success  in  the  case  of  asphalt  base  oils. 
Unless  there  is  a  favorable  structural  condition,  such  as 
a  terrace  or  lenticular  structure,  all  the  chances  are  against 
success  in  drilling  down  dip  in  the  case  of  the  light  oils  of 
Wyoming  and  Colorado.  Asphalt  or  paraffin  met  with  in 
a  drilled  well  at  some  distance  under  the  surface,  is  a  dis- 
tinctly unfavorable  indication,  because  it  proves  that  the 
lighter  hydrocarbons  have  been  evaporated  and  lost  and 
that  only  the  heavy  base  has  been  retained  in  the  rocks. 

"Oil  Shales." 

Oil  shales  are  clay  rocks  rich  in  bituminous  material 
which,  on  destructive  distillation,  yield  oil  and  gas.  Con- 
siderable heat  is  necessary  to  obtain  the  oil.  Probably  by 
far  the  greater  part  is  not  present  as  oil  but  as  an  organic 
residue  which  breaks  up  into  oil  when  heated.  This  is 
corroborated  by  the  fact  that  shales  which  carry  as  much 
as  eighty  gallons  of  oil  to  the  ton,  are  not  in  the  least 
greasy  and  do  not  show  visible  oil.  The  oil  shale  of  the 
Green  River  formation  covers  large  areas  in  northwestern 
Colorado,  southwestern  Wyoming,  and  northeastern  Utah. 
The  shales  are  at  the  earth's  surface  exposed  to  erosion, 
and  have  probably  no  significance  whatever  as  far  as  pos- 
sible oil  fields  are  concerned. 

Oil  and  Gas  Showings  in  Wells. 

Oil  and  gas  in  small  quantities  may  be  disseminated 
through  all  marine  shales,  and  may  be  localized  occasionally 
in  small  porous  streaks  under  conditions  .where  no  commer- 
cial quantities  could  be  expected.  A  showing  of  small 


POPULAR  OIL  GEOLOGY. 


121 


quantities  of  either  oil  or  gas  in  a  well  is,  therefore,  not  a 
necessary  proof  of  the  existence  of,  or  of  approach  to,  an 
oil  pool. 
Summary. 

"Indications"  so  far  mentioned  are  only  of  value  in 
proving  the  fact  that  a  certain  formation  carries  oil.  They 
do  not  indicate  commercial  accumulation  under  the  sur- 
face. Drilling  should  be  undertaken  only  on  a  favorable 
geological  structure  in  rocks  proved  Detroliferous.  The  fol- 
lowing table  of  "indications''  ^moctiliea  after  Craig), 
shows  under  what  conditions  a  formation  may  prove  a  fav- 
orable or  an  unfavorable  one  to  prospect,  provided  a  suit- 
able geological  structure  exists. 


Favorable 


Indications  of  Oil. 
(After  Craig) 


Unfavorable 


Always 

Usually 

Sometimes 

-Usually 

Always 

Shows  of 

Shows  of 

Shows  of 

Evidence 

Shows  of 

oil  and 

filtered 

oil  and 

of  true 

oil  in 

strong 

oil  and 

little 

marine 

thick  po- 

gas in 

gas. 

gas.   • 

conditions. 

rous  beds 

thin 

with  much 

beds  in 

water. 

shales. 

Evidence 

Beds  of 

Gas  shows 

Hot  water 

of  shore 

gypsum 

and  water 

and  no  oil 

conditions. 

and  rock 

in  porous 

or  gas. 

salt. 

beds  in 

shale. 

Shows  of 

Sulphuret- 

Partially 

gas  under 

ted  Hydro- 

evaporated 

thick 

gen  and 

oil  deep 

shales. 

hot  water. 

down. 

Paraffin 

and 

asphalt 

in  surface. 

122  POPULAR  OIL  GEOLOGY. 

Divining  Rod. 

Belief  that  an  oil  pool  can  be  located  by  means  of  the 
divining  rod,  a  forked  willow  twig  or  by  instruments  of 
various  sorts  is  a  survival  of  the  superstition  of  the  middle 
ages  fostered  by  the  charlatan.  There  is  no  scientific  basis 
for  such  belief. 


XII.    Prospecting  and  Developing  Oil  Lands 

Prospecting  for  oil  consists  of  two  distinct  operations ; 
namely,  the  prospecting  for  areas  of  suitable  rocks,  and  the 
locating  of  favorable  structures. 

Prospecting  for  Areas  of  Petroliferous  Rocks. 

In  the  preceding  chapter  "Popular  Fallacies  in  Oil 
Geology",  the  so-called  "Indications"  of  oil  were  discussed 
in  some  detail.  These  include  oil  and  gas  seeps  and 
springs,  the  occurrence  of  salt  water,  the  presence  of  resi- 
dual bases  such  as  asphalt  and  paraffin  at  the  earth's  sur- 
face, and  oil  and  gas  "showings"  in  wells.  None  of  these 
prove  the  existence  of  oil  pools ;  they  are  simply  evidences 
of  the  fact  that  the  rock  formations  carry  petroleum. 
Other  points  have  to  be  considered,  and  their  effect  may  be 
such  as  to  make  an  oil  and  gas  seep  a  distinctly  discourag- 
ing feature. 

Characteristics  of  the  Formation. 

The  problems  of  oil  accumulation  are  intimately  con- 
nected with  the  problem  of  its  origin.  Oil  is  derived  from 
organic  material,  both  plant  and  animal  remains,  which  are 
buried  in  the  finer  sediments,  the  muds,  clays  and  oozes  at 
the  time  of  their  deposition.  Because  of  the  fine  and  dense 
character  of  these  sediments  and  of  the  presence  of  salt 
water,  the  organic  remains  were  protected  from  rapid  de- 
composition and  suffered  only  a  sort  of  selective  putrefac- 
tion which  subsequently  resulted  in  the  formation  of  oil. 
This  change  was  in  part  due  to  increasing  pressure  and 
temperature,  and  in  part  due  to  the  action  of  bacteria.  All 
important  oil  accumulations  are  the  result  of  the  chemical 
or  bacterial  alteration  of  organic  remains.  By  far  the 
greater  part  of  oil  is  formed  in  the  fine  grained  sediments, 
those  that  ultimately  form  shales,  and,  to  a  lesser  extent, 
sandstones. 

123 


124:  POPULAR  OIL  GEOLOGY. 

The  lithological  characteristics  of  the  formations 
within  reach  of  the  drill  are,  therefore,  of  the  utmost  im- 
portance. We  must  know  that  these  rocks  were  originally 
petroliferous,  that  is,  carried  the  raw  materials  from  which 
oil  and  gas  could  be  produced.  Marine  strata,  especially 
those  showing  evidence  of  shallow  water  or  near  shore  con- 
ditions at  the  time  of  their  deposition,  are  the  most  favor- 
able. No  important  accumulations  need  be  expected  in 
rocks  of  strictly  continental  origin. 

Lithological  Characteristics  of  Possible  Reservoirs. 

Another  feature  of  importance  to  be  considered  is  the 
presence  of  suitable  reservoir  rocks  within  or  near  this  for- 
mation and  so  spaced  and  enclosed  as  to  be  capable  of  re- 
taining the  oil  concentrated  in  them.  Without  such  reser- 
voirs it  will  be  impossible  to  concentrate  the  oil  into  a  com- 
mercial pool.  In  possibly  95  per  cent  of  the  producing 
fields  sandstones  or  sands  are  the  reservoirs.  In  any  new 
structure  or  new  field  it  is  of  the  utmost  importance  to 
determine  the  following  features  if  possible : 

A.  Are  the  sandstones  saturated  with  water  ?     This 
will  determine  the  position  of  the  pool  in  the  structure. 
In  dry  sand  the  oil  would  be  in  the  syncline  or  basin.     In 
a  saturated  sand  the  oil  would  be  near  the  crest  of  the  dome 
or  on  the  axis  of  the  anticline. 

B.  Are -the  sands  lenticular  or  continuous?     Lenses 
of  sand  may  too  small  in  area  to  catch  sufficient  oil.   Widely 
distributed  and  continuous  sandstone  beo^  offer  a  large  col- 
lecting surface  to  the  migrating  oil,  a  condition  which  is 
distinctly  favorable.     The  shape  of  the  sandstone  beds  is 
in  many  fields  the  factor  determining  the  accumulation. 

C.  Are  the  sandstones  porous  or  tightly  cemented  ? 
An  open  and  friable  sandstone  has  the  pore  space  available 
to  carry  oil.     Tight  sandstones  may  not  be  worthy  of  con- 
sideration as   possible   reservoirs.      Frequently   there   are 
local  differences  in  the  degree  of  cementation,  and  a  sand 
open  and  porous  in  one  spot  may  be  tightly  cemented  in 
another.    A  realization  of  this  fact  may  make  it  possible  to 
avoid  the  areas  of  induration.     Frequently  this  is  impos- 


POPULAR  OIL  GEOLOGY.  125 

sible,  but  the  knowledge  that  this  feature  prevails  is  of  the 
utmost  importance  to  the  driller. 

D.  Another  feature  to  be  considered  is  the  position 
of  the  sand  with  respect  to  the  petroliferous  formation. 
The  most  effective  migration  of  oil  is  probably  in  a  vertical 
direction  upward.  A  sand  resting  directly  upon  the  petro- 
leum producing  formation  would  therefore  be  in  a  much 
better  position  than  a  reservoir  sand  below  the  series.  This 
is  well  shown  in  Wyoming  by  the  Wall  Creek  sand,  which 
rests  directly  upon  the  marine  shales  of  Benton  age.  These 
shales  are  compact  and  close  grained  sediments  quite  rich 
in  organic  matter,  and  represent  the  most  important  source 
of  the  Wyoming  oils.  At  the  base  of  these  shales  we  have 
the  Muddy  and  the  Greybull  sands.  While  these  carry  oil 
and  gas  locally,  they  are  nowhere  as  productive  as  the  Wall 
Creek  above. 

The  presence  of  more  than  one  sandstone  or  reservoir 
rock  is  an  encouraging  feature.  It  is  of  interest  to  know 
that  the  sandstones  must  be  much  subordinate  in  quantity 
to  the  finer  sediments,  and  that  whenever  the  sands  domi- 
nate, the  likelihood  of  concentration  of  oil  is  decreased.  It 
is  also  well  to  realize  the  fact  that  in  the  same  structure 
certain  sandstones  may  carry  nothing  but  water,  while 
others  may  carry  oil  or  gas  or  a  mixture  of  both.  The  rela- 
tive positions  of  water  and  oil  sands  are  indefinite.  The 
water  horizons  may  be  above  or  below  the  producing  sand 
or  may  be  interbedded  in  a  number  of  such. 

Locating  Structures. 

After  a  favorable  series  of  rocks  has  been  located 
it  is  desirable  to  prospect  them  for  "structures".  This 
necessitates  the  careful  study  of  the  dips  and  strikes  and 
of  the  distribution  of  the  rock  formations  at  the  ^rth's 
surface.  The  latter  is  of  very  great  value  because  Me  dis- 
tribution of  the  formations  at  the  surface  is  dependent 
upon  their  structure. 

Type  of  Structures. 

There  are  two  general  types  of  structures  tending  to 
the  accumulation  of  commercial  oil  pools.  These  are : 


126  POPULAR   OIL   GEOLOGY. 

1.  Trap  Structures. 

2.  Retardation  Structures. 

The  first  structures  are  those  that  effectively  trap  the 
oil  while  migrating  through  the  rocks  and  prevent  further 
migration  as  long  as  these  structural  conditions  exist.  The 
second  type  of  structures  are  such  that  there  is  a  continual 
flow  of  oil  through  them.  The  access  of  new  oil,  however, 
is  greater  than  the  loss,  so  that  the  commercial  accumula- 
tion is  the  result  of  the  retardation  of  the  oil  migration. 
The -structures  of  the  first  class  hold  an  oil  pool  more  or 
less  indefinitely.  The  oil  pool  may  disappear  as  the  result 
of  a  subsequent  structural  disturbance  such  as  igneous  in- 
trusions, complex  folding,  regional  metamorphism  or  ex- 
posure of  the  reservoir  rocks  at  the  surface  by  erosion.  The 
oil  pool  in  the  second  class  of  structure  will  tend  to  disap- 
pear as  soon  as  all  available  oil  is  effectively  concentrated 
along  the  channel  or  direction  of  access.  From  that  time 
on  there  will  be  a  gradual  dissipation  of  the  accumulated 
oil. 

Trap  Structures. 

Trap  structures  carry  the  majority  of  the  important 
accumulations  of  oil.  They  are  not  confined  to  any  partic- 
ular region  or  field  but  are  of  commercial  importance  in 
every  producing  region.  The  following  are  examples  of 
such  structures : 

1.  Domes. 

(a)  Structural  Domes. 

(b)  Saline  Dome, 
(o)   Volcanic  Domes. 

2.  Structural  highs  on  an  anticline. 

3.  Anticline  sealed  by  faults. 
4f    Fissured  rocks. 

5.     Lenticular  sands. 

It  is  well  to  realize  that  such  a  classification  is  not 
lini'd  and  inflexible  and  that  the  accumulations  of  the  oil 
in  such  a  structure  may  be  dissipated  because  of  the  pres- 
ence of  some  interfering  feature  such  as  fractures  and 
faults. 


POPULAR  OIL  GEOLOGY.  127 

Retardation  Structures. 

The  commercial  importance  of  this  class  of  structures 
is  not  nearly  so^great  as  that  of  the  first  class.  In  many 
fields  their  presence  is  of  no  commercial  significance. 
Effective  accumulations  of  oil  in  them  are  restricted  and 
limited  to  certain  fields.  All  these  possess  the  common 
characteristics  of  very  low  dips  and  slight  structural  dis- 
turbances. The  producing  regions  of  North  Central  Texas, 
of  Oklahoma  and  of  Ohio,  are  examples  of  fields  in  which 
these  structures  frequently  carry  oil  pools.  Even  in  these 
regions  we  must  not  lose  sight  of  the  fact  that  trap  struc- 
tures are  the  much  more  likely  to  yield  production.  The 
following  are  examples  of  structures  of  retardation : 

1.  Structural  terraces. 

2.  Changes  in  the  rate  of  dip. 

3.  Structural  valleys  and  ravines. 

4.  Anticlinal  noses. 

5.  Asphalt  sealed  sands. 

Structures  and  Oil  Pools. 

It  is  well  to  realize  that  the  presence  of  a  structure 
does  not  necessarily  indicate  the  presence  of  an  oil  pool. 

The  following  features  must  be  considered  in  deter- 
mining the  likelihood  of  obtaining  production  from  any 
structure : 

1.  Characteristics  of  the  formation. 

2.  The  lithological  character  of  possible  reservoirs. 

3.  Structural  characteristics. 

4.  Geological  history  of  the  area  investigated. 

Topographic  Features. 

The  different  formations  yield  more  or  less  character- 
istic and  distinctive  erosion  forms  which  may  enable  us 
to  recognize  them  at  a  considerable  distance.  This  feature 
is  well  shown  by  the  Mesozoic  rocks  of  the  Bighorn  Basin 
of  Wyoming.  From  the  oil  man's  standpoint,  here  the 
more  important  formations  are  those  included  between  the 
Dakota  and  the  Mesaverde  in  the  columnar  section  on 
page  98»  The  Dakota  sandstone  usually  gives  a  high 
ridge  with  a  sharp  serrated  crest  covered  with  pine  trees. 


128  POPULAR  OIL  GEOLOGY. 

The  Mowry  shale  forms  another  hogback  much  higher  than 
the  Dakota,  marked  with  horizontal  gray  bands  and  char- 
acterized by  smoother  slopes  and  crest.  Part  way  down 
the  dip  slope  of  the  Mowry  hogback  is  a  minor  hogback  of 
sandstone  which  usually  consists  of  two  or  three  well  de- 
nned small  ridges.  This  is  the  Frontier  formation  and 
v  contains  the  most  important  oil  sands  of  the  state.  The 
Cody  shale  forms  a  flat  featureless  valley,  broken  occa- 
sionally by  a  development  of  bad  lands  in  the  rocks  near 
its  base  (Niobrara).  The  Mesaverde  forms  a  high  prom- 
inent hogback  characterized  by  very  thick  massive  ledges 
of  buff  sandstones  and  by  occasional  coal  beds.  These 
topographic  expressions  show  almost  at  a  glance  the  dis- 
tribution of  the  formations  and  hence  the  structure  of  a 
field. 

Folded  areas  usually  follow  mountain  ranges  and  are 
restricted  to  a  narrow  belt  along  the  foot  of  each  range. 
The  longer  axis  of  the  folds  is  usually  parallel  to  the  trend 
of  the  mountain's  uplift.  The  folds  are  unsymmetrical  in 
most  cases,  with  their  steeper  dips  on  the  mountain  sides. 

Choice  of  Structure. 

In  new  and  unproven  territory  it  is  logical  to  test  the 
most  promising  geological  structure  first.  If  possible  this, 
should  be  a  dome,  preferably  one  standing  in  an  isolated 
position  away  from  other  folds,  so  that  a  large  underground 
drainage  area  may  be  tributary  to  it.  Next  favorable  to  a 
dome  is  a  "structural  high"  on  an  anticline.  This  is  fol- 
lowed in  order  by  a  horizontal  anticline,  a  structural  ter- 
race, and  finally  by  faulted  structures  and  unconformities. 

Structural  Characteristics. 

Structural  characteristics  are  of  prime  importance 
in  determining  possibilities  of  accumulation.  The  follow- 
ing characteristics  of  the  structure  should  be  investigated. 

A.     Trap  structures  or  retardation  structures. 

A  structure  of  the  trap  type  is  the  most  favorable  and 
is  equally  so  no  matter  what  field  it  happens  to  be  located 
in.  Structures  of  retardation,  however,  would  not  merit 
consideration  in  those  oil  fields  where  we  have  strong  fold- 


POPULAR  OIL  GEOLOGY.  129 

ing  and  prominent  well  defined  structures,  like  those  of 
the  Rocky  Mountains  and  California.  In  these  fields,  dips 
up  to  the  vertical  occur  and  the  circulation  of  water  pro- 
ceeds so  readily  that  the  retardation  in  flow  due  to  a  ter- 
race or  structural  ravine  is  usually  insufficient  to  hold  the 
oil  in  large  enough  quantities  to  merit  exploitation.  It  is 
well  to  regard  such  structures  with  suspicion  in  all  fields 
except  those  with  very  low  dips. 

B.     Surface  and  sub-surface  structures. 

Very  frequently  it  happens  that  a  structure  shown  at 
the  surface  disappears  in  depth.  In  other  cases  it  may  be- 
come accentuated.  This  is  due  to  the  fact  that  the  strata 
are  not  absolutely  parallel  but  converge  more  or  less  rap- 
idly. This  may  be  due  to  the  fact  that  the  sedimentary 
formations  are  lenticular,  or  it  may  be  due  to  the  fact  that 
they  are  unconformable  to  each  other.  Thus,  the  underly- 
ing rocks  which  carry  the  oil  may  have  been  folded  previ- 
ous to  the  deposition  of  the  surface  rocks.  Subsequent  to 
the  deposition  of  the  latter,  the  rocks  may  have  been  folded 
once  more  along  the  same  general  axis,  thereby  intensify- 
ing the  fold  in  the  lower  formation.  In  the  Northern  part 
of  the  Gulf  Coastal  Plains,  as  at  Homer,  Louisiana,  Corsi- 
cana,  Texas,  and  also  in  the  North  Central  Texas  fields,  as 
at  Burkburnett  and  Desdemona,  there  are  only  very  slight 
structural  disturbances  in  the  rocks  at  the  surface  but  a 
much  accentuated  folding  in  the  oil  sands  below. 

In  other  regions  the  relationship  of  the  surface  forma- 
tions to  the  underlying  oil  producer  may  be  such  that  an 
apparently  favorable  structure  in  them  is  of  no  value. 
Thus,  the  structures  in  the  Tertiary  formations  of  the 
Rocky  Mountain  region  ordinarily  afford  no  clue  as  to  the 
attitude  of  the  Cretaceous  or  older  rocks  below. 

Relation  to  Other  Structural  Features. 

The  oil  structure,  while  favorable  in  form,  may  be  so 
located  as  to  preclude  any  expectation  of  large  production. 
Thus,  for  example,  in  the  Kansas  oil  fields  the  general  dip 
of  the  formations  is  westward  and  the  important  drainage 
direction  from  which  the  oil  comes  is  from  the  West.  A 


130  POPULAR  OIL  GEOLOGY. 

structure  that  is  located  immediately  to  the  east  of  another 
structure  has,  therefore,  a  somewhat  unfavorable  position, 
because  the  drainage  from  the  west  will  be  interrupted  by 
the  latter  structure,  and,  if  this  be  large  enough,  it  may 
trap  and  hold  all  the  available  oil. 
Geologic  History. 

Certain  features  of  geologic  history  influence  produc- 
tivity of  an  oil  field.  The  date  of  folding  or  of  formation 
of  the  structure  is  of  considerable  significance.  Tf  the  fold- 
ing followed  closely  the  period  of  the  deposition  of  the 
rocks  it  will  be  much  more  favorable  than  if  a  long  period 
of  time  had  previously  elapsed.  In  the  latter  case  there 
will  be  less  tendency  for  a  concentration  of  the  oil.  In 
the  first  case  it  might  be  concentrated  as  quickly  as  formed. 
The  conditions  following  the  deposition  of  the  sediments 
are  the  conditions  under  which  the  formation  of  oil  must 
have  taken  place.  A  great  deal  of  volcanic  and  igneous 
activity  with  its  attendant  structural  disturbance  .tend  to 
dissipate  the  oil.  A  limited  amount  of  igneous  intrusions 
would  hasten  distillation  with  a  probable  formation  of  a 
heavy  black  oil.  Much  structural  disturbance  would  have 
the  tendency  to  convert  the  oil  into  gas.  The  degree  of 
metamorphism  determines  the  likelihood  of  finding  petro- 
leum. Excessive  n^etamorphism  is  unfavorable.  Meta- 
morphism is  a  function  of  both  age  and  pressure  and  con- 
sequently of  structural  disturbance.  The  greater  the  struc- 
tural disturbance  and  the  greater  the  age,  the  more  pro- 
nounced the  metamorphism.  David  White  has  suggested 
that  since  the  nature  of  the  coals  associated  with  oil-bearing 
rocks  depends  upon  the  stage  of  the  metamorphism  to 
which  it  has  been  subjected,  the  coals  may  servo  as  a  cri- 
terion to  measure  its  intensity.  It  has  been  found  that  the 
percentage  of  carbon  in  coal  increases  with  the  amount  of 
intensity  of  the  metamorphism  to  which  it  has  been  sub- 
jected. When  the  percentage  of  carbon  in  coal  exceeds  05 
per  cent  no  production  need  be  expected.  Most  of  the  im- 
portant accumulations  of  oil  occur  in  regions  where  the 
percentage  of  carbon  in  coal  is  less  than  55  per  cent.  It  is 
well  to  carry  in  mind  the  fact  that  this  generalization  ap- 


POPULAR  OIL  GEOLOGY. 


131 


plies  only  to  the  formation  in  which  the  coal  itself  occurs 
and  cannot  be  applied  to  much  younger  and  overlying  rocks. 

Summary. 

From  the  theoretic  considerations  discussed  above,  it 
will  be  apparent  that  the  following  features  will  favor 
maximum  accumulation  of  oil : 

1.  Comparatively  recent  age  of  formations. 

2.  Slight  folding,  very  closely  following  the  period 

of  deposition. 

3.  Rock  originally  rich  in  organic  remains. 

Great  geologic  age,  excessive  and  intense  folding,  tend 
to  the  carbonization  of  the  oil  and  to  the  production  of  gas. 
Rocks  rich  in  fossils  are  not  necessarily  rocks  rich  in  or- 
ganic remains.  The  shells  of  clams  and  oysters  may  ac- 
cumulate in  tremendous  quantities  without  any  accompany- 
ing preservation  of  the  fleshy  part  of  these  animals.  The 
presence  of  fossils,  therefore,  does  not  prove  the  presence 
of  oil. 

Locating  a  Test  Well. 

The  location  of  the  test  well  is  of  the  utmost  import- 
ance. In  nearly  all  cases  this  should  be  located  near  the 
highest  point  of  the  structure.  In  most  oil  fields  the 
reservoir  rocks  are  saturated;  the  highest  part  of  the  fold 
should,  therefore,  be  productive.  In  case  a  well  so  located 
strikes  water,  the  structure  is  probably  nonproductive. 
Should  the  well  strike  gas,  a  second  well  should  be  drilled 
down  dip  on  the  flank  of  the  fold  where  the  oil  would  be 
expected.  A  dry  hole  in  the  apex  of  an  anticline,  where 
an  examination  of  the  drillings  from  the  reservoir  rock 


Figure  49.     Dome  left  as  structural  mountain. 


132 


POPULAR  OIL   GEOLOGY. 


proves  this.to  be  porous  and  open,  indicates  a  dry  sand  or 
at  least  only  a  partially  saturated  one.  Therefore  the  next 
test  well  should  be  located  down  on  the  flanks  of  the  fold 
or  on  the  syncline. 


Figure  50.     Eroded   dome. 

To  locate  the  highest  point  on  a  particular  structure 
is  not  as  simple  as  it  would  appear  to  be.  The  dome  or 
anticline  may  be  left  as  an  elevation  due  to  the  presence 
of  a  resistant  layer  of  rock.  The  highest  point  of  this 
elevation  may  represent  the  apex  of  the  structure.  This 
is  frequently  the  case  in  Oklahoma.  Wyoming  oil  domes 
are  usually  so  eroded  as  to  show  a  central  basin  surrounded 
by  encircling  hogbacks  of  the  harder  rocks.  Consequently 
here  the  surface  elevation  has  no  significance.  The  lowest 
point  in  the  surface  may  actually  represent  the  highest 
point  in  the  structure.  An  instrumental  survey  may  be 
needed  to  determine  the  axis  or  apex  of  low,  flat-dipping 
structures  that  cover  large  areas. 


Figure  51.     Sections  to  show  the  relationship  existing  between 
width  of  producing  area  and  dip  of  rocks. 


POPULAR  OIL  GEOLOGY.  133 

In  structures  with  steep  dips  the  productive  surface 
area  is  of  limited  extent,  and  the  correct  location  of  test 
wells  is  of  paramount  importance.  The  axis  of  an  un- 
symmetrical  anticline  shifts  in  the  direction  of  minimum 
dip  with  descent.  A  test  well  must,  therefore,  be  located 
away  from  the  surface  axis  on  the  side  of  least  dip.  Its 
location  must  be  carefully  determined  in  order  to  ensure 
its  striking  the  oil  sand  at  the  top  of  the  fold. 

Economic  Considerations. 

It  is  of  course  self  evident  that  certain  economic  con- 
siderations are  of  the  utmost  importance  in  determining 
the  advisability  of  drilling  a  particular  structure.  Indeed, 
these  may  be  more  important  than  geologic  considerations 
and  may  make  inadvisable  the  development  of  an  area 
otherwise  favorable.  Those  individuals  and  corporations 
using  the  nicest  of  judgment  in  balancing  these  two  sets  of 
considerations  against  each  other  achieve  the  greatest  suc- 
cess in  the  petroleum  industry. 

The  economic  considerations  may  be  grouped  under 
the  following  headings : 

1.  Depth  of  drilling. 

2.  Possible  value  of  production. 

3.  Accessibility. 

4.  Transportation  facilities. 
Operating  requirements. 
Legal  status  of  lands. 

Depth  of  Drilling. 

The  post  of  operation  increases  rapidly  with  increas- 
ing depth.  Whenever  the  depth  exceeds  3,000  feet,  the 
cost  of  operation  increases  at  a  startling  rate.  The  writer 
doubts  that  a  3,000  foot  wild-cat  well  can  be  drilled  in  the 
Eockies  for  less  than  100,000  dollars.  In  North  Central 
Texas  a  similar  hole  -could  perhaps  be  drilled  for  one-half 
this  amount.  In  the  Gulf  Coastal  Plains,  by  using  a  ro- 
tary, the  cost  can  probably  be  reduced  to  30,000  dollars. 
Each  additional  thousand  feet  will  approximately  double 
the  cost  of  the  well.  Excessive  depth  to  possible  oil  sands 
may  make  a  structure  unattractive. 


134  POPULAR  OIL  GEOLOGY. 

Possible  Value  of  Production. 

Seeps,  outcrops  of  sands  at  the  surface,  records  of  other 
wells  or  other  geologic  features,  may  indicate  the  nature 
of  the  production  to  be  expected.  Probabilities  may  be  in 
favor  of  gas  or  bla<5k  oil  or  light  paraffin  oil.  It  may  also 
be  possible  to  form  a  conclusion  as  to  the  approximate  mag- 
nitude of  the  probable  yield.  Such  conclusions  are  always 
dangerous  especially  in  wild  cat  areas,  and  should  only  be 
received  with  credulence  when  made  by  geologists  of  wide 
experience  and  when  backed  by  all  the  observed  facts  in 
the  area  under  investigation.  It  is  not  possible  to  foretell 
the  exact  amount  of  the  production  to  be  expected  from  any 
well.  Such  forecasts  are  in  a  class  with  the  request  of  a 
newcomer  in  the  oil  game,  who  asked  drilling  contractors 
to  submit  bids  on  the  cost  of  drilling  a  hundred-barrel  well. 

Accessibility. 

Accessibility  to  labor  markets,  to  supplies  needed  in 
drilling  and  development,  to  fuel  and  water,  determine  in 
part  the  cost  of  operations.  Many  areas  may  be  so  far  dis- 
tant from  markets  and  supply  houses  that  a  great  deal  of 
expensive  and  little  used  machinery  and  tools  must  be  kept 
on  hand  to  provide  for  possible  emergencies  that  may  never 
arise. 

Transportation  Facilities. 

To  some  extent  transportation  facilities  and  accessibil- 
ity go  hand  in  hand.  The  presence  of  railroad  lines  facil- 
itates and  cheapens  costs.  Many  of  the  western  areas  fav- 
orable from  the  geological  standpoint  are  without  adequate 
railroad  facilities.  Transportation  costs  become  exorbi- 
tant, when  all  materials,  supplies  and  fuel-  must  be 
handled  by  auto  or  team  over  poor  roads,  possibly  fifty  to 
one  hundred  miles  from  the  railroad.  In  many  cases  roads 
must  be  built  and  maintained  -and  even  the  water  needed 
for  drilling  in nst  bo  hauled  many  miles.  Under  such  con- 
ditions development  is  seriously  handicapped,  not  only  be- 
cause of  the  high  cost  of  drilling,  but  also  because  of  the 
exorbitant  cost  of  marketing  the  oil  produced. 


POPULAR  OIL  GEOLOGY.  135 

Operating  Requirements. 

The  requirements  of  drilling  and  operating  and, the 
royalties  stipulated  by  the  leases  may  be  of  such  a  nature 
as  to  destroy  the_  attractiveness  of  a  promising  acreage. 
Legitimate  concerns  will  not  sign  contracts  to  drill  twenty 
wells  on  a  wild-cat  structure ;  neither  will  they  pay  40  per 
cent  royalty.  Demands  such  as  these  may  be  met  on  paper 
by  promoters  of  stock  sales  propositions.  Property  owners 
should  realize  the  fact  that  one-eigth  royalty  is  the  accepted 
standard  established  as  the  basis  of  a  fair  working  agree- 
ment between  the  producer  and  the  property  owner.  High 
royalties  quickly  destroy  the  margin  of  profit  to  the  pro- 
ducer. The  incentive  is  to  speed  up  production  and  to 
abandon  the  property  before  it  is  really  exhausted.  Thus, 
the  result  is  an  economic  loss  to  the  nation  and  potentially 
a  financial  loss  to  the  operating  company  and  the  land 
owner.  The  drilling  of  wells  and  the  production  of  oil  is  a 
legitimate  place  of  business  activity.  Experience  has  es- 
tablished principles  of  conduct  and  conditions  of  operation 
which  cannot  be  violated  without  incurring  the  danger  of 
bankruptcy. 

Legal  Status  of  Land. 

Operators  should  assure  themselves  that  the  title  to 
the  land  is  clear  and  valid.  All  conflicting  titles,  no  matter 
how  flimsy,  should  be  cleared  up  and  settled  preceding  de- 
velopment. After  discovery  of  oil  in  commercial  quanti- 
ties, these  can  probably  not  be  settled  except  by  expensive 
and  perhaps  drawn-out  litigation. 

Title  of  much  of  the  prospective  oil  land  in  the  West 
conies  direct  from  the  government  in  the  form  of  oil  placer 
claims.  In  many  cases  a  number  of  different  claimants 
have  located  the  same  acreage.  In  these  cases  it  requires 
the  nicest  of  legal  acumen  to  determine  the  valid  title.  It 
appears  to  be  the  concensus  of  opinion  that  the  claimant 
first  discovering  oil  in  commerical  quantities  has  best  title. 

Much  of  the  land  is  homestead  land  taken  up  by  the 
agricultural  claimant  under  a  specific  waiver  of  mineral 


136  POPULAR  OIL  GEOLOGY. 

rights  which  are  expressly  reserved  to  the  Government  sub- 
ject to  future  legislation.  Leases  from  the  homesteader 
appear,  therefore,  to  be  invalid.  Oil  placer  claims  are  fre- 
quently filed  over  such  homesteads  with  or  without  the  con- 
sent of  the  homesteader.  Their  status  is  doubtful,  although 
the  title  may  be  the  best  obtainable  under  the  conditions. 

Much  of  the  Government  land  in  the  West  is  located 
on  areas  withdrawn  from  entry  as  oil  land.  The  largest 
of  these  areas  are  located  in  Wyoming  and  California. 
Their  disposition  is  subject  to  future  legislation  such  as 
the  "oil  land  leasing  bill"  now  before  Congress.  According 
to  the  features  of  this  bill,  the  land  would  be  leased  directly 
from  the  Government  on  a  royalty  basis,  subject  to  certain 
limi  tations  as  to  the  area  of  land  so  obtainable. 

Producing  Problems. 

It  has  been  well  stated  by  Hager  that  the  problem 
of  the  producer  consists  of  three  distinct  and  separate 
parts.  First,  he  must  work  out  the  best  method  of  pro- 
duction for  his  property;  second,  the  best  method  of  de- 
fending it  against  drainage  by  neighboring  producers ;  and 
third,  the  most  effective  method  of  draining  adjacent  prop- 
erties. These  ideas  must  be  constantly  carried  in  mind 
because  oil  reservoirs  are  more  or  less  continuous  sheets 
that  underlie  large  areas,  and  a  few  favorably  located 
wells  will  in  the  course  of  time  seriously  affect  and  even 
destroy  the  possibilities  of  production  in  adjacent 
properties. 

Objects  of  Production. 

Maximum  profit  with  least  expense  is  the  chief  object 
of  most  producers.  This  does  not  imply  the  production  of 
the  greatest  quantity  of  oil  possible  from  a  given  area 
because  the  element  of  time  must  be  considered.  Thus  it 
is  possible  to  speed  up  production  so  as  to  secure  a  large 
annual  production  for  a  short  time.  A  rapid  return  of 
the  capital  invested  and  a  high  profit  is  the  result.  More 


POPULAR  OIL  GEOLOGY. 


137 


Figure  52.    Section  of  an  unsymmetric  anticline,  illustrating  the 
shift  of  the  crest  of  the  fold  with  increasing  depth. 

economic  and  less  wasteful  methods  would  yield  a  smaller 
annual  production  spread  over  a  proportionately  greater 
period  of  years,  so  that  eventually  a  much  larger  quantity 
of  oil  would  be  obtained  from  the  same  area.  The  return 
of  the  money  invested  is  slower  in  this  case  and  the 
annual  profits  are  much  smaller.  In  most  oil  fields  the 
methods  adopted  are  strictly  those  of  the  first  class.  Every 
attempt  is  made  to  produce  as  much  oil  as  possible  in  the 
least  time  from  a  given  plot  of  ground.  . 

Spacing  of  Wells. 

The  rate  of  production  depends  mainly  on  the  loca- 
tion and  spacing  of  wells.  Best  practice  means  drilling 
one  well  for  every  five  to  ten  acres.  The  spacing  best 
suited  to  a  particular  area  can  be  determined  by  a  con- 
sideration of  the  following  points: 

1.  The  amount  of  oil  available. 

2.  The  rate  of  flow  or  circulation  of  oil. 

3.  The  methods   adopted  by  neighboring  pro- 

ducers. 

Amount  of  Oil  Available. 

The  amount  of  oil  available  can  be  determined  from 
the  following: 

(a)  The  number  of  oil  sands  in  reach  of  the 

drill. 

(b)  Their  aggregate  thickness. 

(c)  Their  degree  of  saturation. 


138  POPULAR  OIL  GEOLOGY. 

The  number  of  oil  sands  and  their  aggregate  thick- 
ness is  determined  by  a  study  of  the  columnar  section  and 
of  well  records.  The  degree  of  saturation  depends  on  the 
field.  The  average  is  about  ten  per  cent  by  volume;  this 
means  a  potential  production  of  about  five  hundred  bar- 
rels per  acre  foot.  The  saturation  of  Wyoming  sands  is 
probably  greater  than  this  because  of  their  open  porous 
structure.  Calculations  should  be  based  only  on  that  part 
of  the  area  actually  underlain  by  the  oil  pool.  The  greater 
the  quantity  of  oil  present,  the  closer  the  wells  may  be 
spaced  without  injury  to  the  field. 

Flow  of  Oil. 

The  relative  ease  of  flow  is  dependent  on 

(a)  The  character  of  the  reservoir  rock. 

(b)  The  viscosity  and  specific  gravity  of  the 

oil. 

(c)  The  steepness  of  the  dip. 

(d)  The  pressure  on  the  oil. 

Ready  circulation  is  favored  by  a  reservoir  that  is 
open  and  contains  pores  that  are  large,  continuous,  and 
connected.  A  reservoir  of  low  porosity  with  small,  tortuous 
and  disconnected  openings  retards  the  flow  of  oil  and  neces- 
sitates a  closer  spacing  of  wells.  Viscous  oils  flow  with 
difficulty.  Other  conditions  being  the  same,  wells  should 
be  spaced  closer  in  fields  producing  a  heavy  asphalt  oil 
and  farther  apart  in  those  fields  that  produce  a  high  grade 
paraffin  base  oil.  The  steepness  of  the  dip  determines  the 
gradient  of  flow.  It  is  evident,  therefore,  that  steep  dips 
are  conducive  to  easy  and  rapid  flow.  Flat  dips  retard 
flow.  The  steeper  the  dip  the  less  number  of  wells  are  re- 
quired to  drain  a  given  area.  The  methods  adopted  in  the 
drilling  of  adjacent  properties  must  influence  every  drill- 
ing campaign.  These  call  for  defensive  methods  and  are 
discussed  under  that  heading. 


POPULAR    OIL.    GEOLOGY. 


139 


Figure   53.     Flowing  well,   Salt  Creek  Field. 

(U.  S.  Geol.  Sur.) 

Defensive  and  Offensive  Methods. 

.  "A  good  offensive  is  the  best  defensive".  This  is 
true  in  oil  production  as  well  as  in  warfare.  For  this 
reason  both  methods  may  be  considered  simultaneously. 

Every  well  drains  oil  from  an  area  the  shape  and 
size  of  which  depends  on 

(a)  The  ease  of  flow  of  the  oil. 

(b)  The  dip  of  the  oil  reservoir. 

(c)  The  location  of  other  wells. 

(d)  The  extent  of  the  pool. 

With  horizontal  or  nearly  horizontal  reservoirs  the 
area  drained  by  a  single  well  will  be  nearly  circular  in 
outline  with  the  well  located  at  the  center.  Ready  and 
easy  flow  of  oil  increases  the  size  of  the  area.  This  has 
been  mentioned  under  "Spacing  of  Oil  Wells".  In  steeply 
dipping  reservoirs  the  area  drained  assumes  an  elliptical 
shape,  with  the  longer  diameter  in  the  direction  of  the 
dip.  The  well  is  not  located  at  the  center  of  the  ellipse 


140  POPULAR  OIL  GEOLOGY. 


B 


o          o          o 
A      . 

Figure  54.  Defensive  tactics.  B  is  drilling  offset  wells. 
but  on  the  down-dip  side,  because  of  readier  flow  in  this 
direction.  Other  producing  wells,  if  located  near  enough, 
limit  the  area  for  drainage  by  another  well.  Such  wells 
are  especially  effective  if  located  along  the  dip;  less  so  if 
located  along  the  strike.  The  drainage  area  of  a  well  is, 
of  necessity,  limited  by  the  extent  of  the  pool.  Wells 
located  at  the  edges  of  pools  must  derive  their  oil  from 
areas  very  much  restricted  as  compared  to  wells  on  inside 
locations.  Their  capacity  is,  therefore,  much  smaller. 

Offsetting. 

As  is  evident  from  this  discussion,  the  drainage  area 
of  any  well  follows  natural  laws  and  not  artificial  boun- 
daries. Oil  wells  located  directly  on  the  line  between  two 
properties  will  drain  areas  of  both.  Indeed,  they  may  be 
so  situated  that  the  greater  part  of  their  drainage  area 
lies  in  the  adjacent  property  instead  of  the  one  in  which 
the  well  is  located.  This  is  true  if  the  well  is  placed  down- 
dip  from  the  adjacent  property.  It  will  be  apparent  that 
a  tract  of  land  may  be  surrounded  by  oil  wells  on  all  sides 
and  be  completely  drained  without  ever  having  a  produc- 
ing well  drilled  on  it.  To  defend  a  property  against 
drainage  by  adjacent  wells,  "offset"  wells  are  drilled. 
These  are  wells  directly  across  the  boundary  line  from  the 
producing  well.  Their  spacing  and  that  of  subsequent 
wells  is  shown  on  figure  54.  The  most  effective  offset 
wells  are  those  located  down  the  dip  of  the  formation,  or 
down  the  pitch  of  the  axis  from  a  producing  well.  In 
addition  to  drilling  offset  wells,  it  is  also  desirable  to 
drill  wells  of  larger  diameter,  because  the  larger  the  well 


POPULAR  OIL  GEOLOGY.  141 

the  greater  the  producing  capacity.  It  is  also  possible  to 
speed  up  production  from  the  line  wells,  which  will  result 
in  a  gain  in  oil  production  at  the  expense  of  the  adjacent 
property. 


XIII.   Oil  Stales  and  Tlieir  Utilization 

The  constantly  increasing  consumption  of  crude  oil  in 
the  United  States  is  a  cause  of  serious  concern.  This  is 
due  to  the  fact  that  the  older  oil  fields  are  being  exhausted 
rapidly,  and  that  no  new  oil  fields  of  great  importance 
have  been  discovered  in  the  last  few  years  in  spite  of  very 
vigorous  prospecting  campaigns.  At  the  present  rate  of 
consumption  all  the  known  oil  fields  of  the  United  States 
will  be  exhausted  within  the  next  twenty  years.  For  these 
reasons  there  is  much  interest  in  "oil  shales''  as  a  possible 
source  of  petroleum. 

Oil  Shales. 

Oil  shales  are  shales,  that  is,  muds  or  clays  consoli- 
dated into  rocks,  from  which  oil  and  gas  can  be  produced 
by  destructive  distillation.  These  shales  do  not  actually 
carry  oil  or  gas  as  such.  They  contain  organic  materials 
such  as  partially  altered  plant  remains  which  are  broken 
up  into  oil  and  gas  when  subjected  to  heat.  That  by  far 
the  greater  part  of  the  oil  is  not  present  as  such  is  proved 
by  the  fact  that  even  the  richest  shales  are  not  greasy  or 
oily  in  appearance,  and  that  oil  seeps  are  virtually  un- 
known in  them. 

Location. 

Probably  the  most  extensive  and  richest  deposits  of 
oil  shale  occur  in  northwestern  Colorado,  southwestern 
Wyoming,  and  northeastern  Utah.  The  area  covered  is 
shown  on  the  accompanying  map. 

Oil  Content. 

It  is  estimated  that  the  oil  shale  in  Colorado  alone 
carries  ten  times  as  much  oil  as  all  the  oil  fields  in  the 
United  States  have  produced  since  1859.  The  areas  in 
Wyoming  and  Utah  that  are  underlain  by  oil  shale  are 
as  large  as  those  in  Colorado,  and  those  in  Utah  are  un- 
doubtedly just  as  rich. 

142 


POPULAB  OIL  GEOLOGY. 


143 


Figure  55.     Map  showing  Colorado  and  Utah  oil  shales. 

(U.  S.  Geol.  Sur.) 

Green  River  Formation. 

The  oil-bearing  shale  is  confined  to  the  middle  part  of 
the  Green  River  formation.  This  is  of  Tertiary  age.  In 
the  Colorado  shale  area,  this  lies  at  the  earth's  surface. 
In  Utah  and  Wyoming,  the  Green  River  shale  is  covered 
for  a  greater  part  by  younger  rocks. 


144 


POPULAR  OIL  GEOLOGY. 


The  Green  River  formation  is  essentially  shale. 

"It  exhibits  on  the  weathered  outcrop  a  more  or 
less  white  color,  but  closer  examination  reveals  an 
alternation  of  gray,  bluish  gray,  and  white  bands. 
The  shale  that  yields  the  most  oil  when  subjected  to 
distillation  is  that  which  weathers  into  massive  benches 
of  grayish-blue  color  but  which  is  dark  brown  to 

SHALE 

CRUSHErR 

(ginch) 

RETORTS 


^^ 
SPENT  SHALE 


OI&, 


COMBUSTIBLE  CA5E5 
AMMONIA  &  WATER  VAPOR 


AMMONIAWATER 


WATE;R  HEATER 
CONDENSER 

LIQUIDS  &  GASES 

I 
SEPARATORS 

OAS,  NAPHTHA 
&  AMMONIA 

WATER  SCRUBBER 


AMMONIA 
AMMONIUM  SULPHATE  PLANT 

GAS 
FUEL  FOR  RETORTS 


DE,  OIL 

REFINERY 

&<  NAPHTHA 


IL  SCRUBBER. 

OIL 
NAPHTHA  PI  ANT 


Figure  56.     Outline  of  treatment  of  oil  shale. 


black  on  a  freshly  broken  surface.  After  this  tough 
rich  shale,  which  appears  to  be  without  bedding 
planes  or  laminations,  is  heated  and  the  oil  driven 
off  it  crumbles  easily  and  exhibits  true  shale  struc- 
ture. Where  thin  benches  of  rich  shale  are  inter- 
bedded  with  lean  or  barren  shale,  the  former,  being 
resistant,  weathers  to  projecting  ledges.  Some  of  the 


POPULAR  OIL  GEOLOGY.  145 

very  rich  beds  show  a  vitreous  luster  similar  to  that 
of  coal.  The  massive  shale  is  exceedingly  tough,  re- 
sists erosion  to  a  remarkable  degree,  and  as  it  weathers 
to  a  bluish-white  surface  and  will  burn  when  ignited 
the  ranchers  of  some  parts  of  the  region  refer  to  it  as 
'white  rock  that  will  burn.'  When  freshly  broken, 
the  shale  gives  off  an  odor  of  petroleum.  All  grada- 
tions exist  between  this  hard,  tough,  massive  rock 
and  the  papery  shale  which  weathers  to  curly  forms. 
The  papery  shale  is  in  a  few  places  black,  but 
usually  light  brown,  and  the  thin  plates  of  weathered 
shale  are  remarkably  flexible,  a  characteristic  which 
distinguishes  it'  from  ordinary  carbonaceous  shale. 
Weathering  affects  the  papery  shale  to  a  distance  of 
more  than  twenty  feet  back  from  the  outcrop,  but, 
except  along  joint  planes,  the  hard,  massive  shale 
shows  little  evidence  of  weathering  for  more  than  a 
quarter  of  an  inch  from  the  exposed  surface.  Oil  has 
been  distilled  from  the  papery  shale  as  well  as  from 
the  hard,  massive  variety,  although  in  smaller  quan- 
tity. The  hard,  rich  shale  that  crops  out  as  project- 
ing ledges  and  weathers  to  a  gray  or  grayish-blue 
color  is  dark  brown  to  black  on  the  unweathered  sur- 
face, and  in  all  probability  weathering  does  not  affect 
the  oil-yielding  capacity  of  the  shale  to  any  con- 
siderable depths." 

The  whole  formation  varies  from  two  thousand  to 
about  twenty-six  hundred  feet  in  thickness.  Not  all  of  the 
formation  is  valuable  as  oil  shale.  This  occurs  in  layers 
from  a  fraction  of  an  inch  up  to  twenty  feet  in  thickness. 

Distillation  Tests. 

The  shale  yields  in  addition  to  oil  and  gas,  large  quan- 
tities of  ammonium  sulphate.  This  is  quite  valuable  as  a 
fertilizer.  The  accompanying  table  shows  the  results  of 
distillation  tests  of  a  number  of  different  shale  beds  in 
the  Green  River  formation. 


146  POPULAR  OIL  GEOLOGY. 

Analyses  of  Shale  Oils  and  Oil  Shales. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

Distillation 

Tests  — 

Gasoline 

10.0 

12.0 

12.0 

6.0 

11.0 

7.0 

10.5 

9.0 

9.0 

Kerosene 

28.5 

32.0 

49.0 

35.0 

35.5 

39.0 

42.5 

35.5 

38.5 

Residuum 

61.5 

56.0 

39.0 

59.0 

53.5 

54.0 

47.0 

51.5 

52.5 

Specific  Grav- 

ity at  60°  F. 

Crude 

0.8937 

0.8850 

0.9138 

0.9290 

0.9327 

0.8946 

0.8838 

0.9126 

0.9126 

Gasoline 

0.7947 

0.7769 

0.8090 

0.7974 

0.8202 

0.7849 

0.7568 

0.7838 

0.7605 

Kerosene 

0.8602 

0.8466 

0.8260 

0.8742 

0.8876 

0.8722 

0.8524 

0.8682 

0.8538 

Residuum 

0.9695 

0.9643 

0.9884 

0.9894 

1.0160 

0.9684 

0.9368 

0.9695 

0.9628 

Asphalt, 

percent. 

1.35 

0.82 

2.82 

4.10 

3.62 

2.49 

0.47 

1.40 

1.03 

Paraffin, 

percent. 

7.70 

6.93 

2.22 

3.72 

1.63 

4.56 

4.70 

9.21 

4.00 

Sulphur, 

percent 

0.54 

1.06 

0  73 

1  42 

0  41 

0  69 

Nitrogen, 

percent. 

1.848 

0.887 

2.198 

1.549 

1.643 

1.267 

1.849 

1.820 

2.135 

Analyses    of 

Shale  — 

Proximate 

Moisture 

1  05 

1  05 

3  18 

0  45 

0  43 

0  85 

Volatile 

Matter 

33.55 

45.04 

19.55 

32.90 

39.85 

51.60 

Ash 

65  43 

45  73 

79  00 

62  65 

59  95 

46  23 

Ultimate— 

Sulphur 

0  27 

1  07 

1.08 

0  55 

0  30 

0  95 

Hydrogen 

1.80 

5.19 

1.75 

2.76 

2.24 

4.32 

Carbon 

13  37 

36  76 

8.34 

22.48 

18.87 

36.40 

Nitrogen 

0.39 

0.39 

0.46 

0.54 

0.46 

1.22 

18  74 

10  86 

9  37 

11  02 

18  18 

10  88 

Yield  of  Shale, 

gallons    ton 

16.8 

86.8 

11.3 

on    Q  o 

Z  J.oo 

6.27 

8.4 

40.6 

28.0 

65.3 

The  fractional  cut  of  shale  oil  given  in  most  analyses 
under  the  heading  of  "gasoline"  or  "motor  fuel"  is  not 
gasoline  suitable  for  the  ordinary  internal  combustion  en- 
gine. •  It  is  a  very  complex  distillate  and  only  a  small  frac- 
tion of  it  can  be  refined  into  commercial  gasoline. 


POPULAR  OIL  GEOLOGY. 


147 


"The  following  figures'*  are  based  on  the  results  of 
one  hundred  and  thirty-two  analyses  published  by  the 
United  States  Geological  Survey,  forty- two  analyses  made 
in  the  laboratories  of  the  Colorado  School  of  Mines,  and 
thirty-one  analyses  from  other  sources.  Fifty-four  of  the 
analyses  are  on  Colorado  shales,  fifty-two  on  Utah  shales, 
forty-five  on  Wyoming  shales,  and  fifty-four  on  Nevada 
shales. 


No.  of 
Analyses 

Constituent 

Unit 

Average 

205 
205 
163 
64 
26 
26 
26 
16 
6 

Shale  Oil 
Shale  Oil 
Ammonium  Sulphate 
Gas 
Water 
Spent  Shale 
Sulphur 
Heating  Value 
Carbon 

Gallons  per  Ton 
Specific  Gravity 
Pounds  per  Ton 
Cubic  Feet  per  Ton 
Gallons  per  Ton 
Pounds  per  Ton 
Percent 
B.  t.  u. 
Percent 

38.0 
.890 
9.4 
3800. 
4.8 
1200. 
.80 
4500. 
22.5 

" Shale  distillations  with  steam  yield  a  few  more  gal- 
lons of  oil  a  ton  than  dry  distillations,  and  the  specific  grav- 
ity of  the  oil  is  between  .03  and  .04  greater.  Steam  distill- 
ations also  increase  the  quantity  of  ammonium  sulphate 
between  two  and  three  times  the  value  obtained  by  the  dry 
distillation.  The  values  given  in  the  table  above  were  ob- 
tained by  dry  distillation.  In  the  laboratory  distillations, 
the  yield  of  gas  is  almost  doubled  if  the  retort  is  sur- 
rounded by  magnesia  insulation,  and  the  final  temperature 
is  thus  increased  a  few  hundred  degrees." 

Shale  Oil. 

"Shale  oils  vary  considerably  in  color,  specific  gravity, 
and  viscosity,  and  in  their  content  of  sulphur,  asphalt,  and 
paraffin.  They  invariably  contain  a  larger  percentage  of 
unsatu rated  hydrocarbons  than  petroleum.  This  is  quite 
a  disadvantage  in  their  utilization  for  gasoline,  but  im- 
provement in  motors  and  methods  of  refining  may  largely 
overcome  this  handicap.  Experiments  in  cracking  the 
heavier  distillates  from  shale  oil  show  that  it  is  possible 
in  this  way  to  increase  the  yield  of  gasoline.  The  follow- 

*  Quoted  from  article  by  C.  W.  Botkin. 


148 


POPULAR    OIL    GEOLOGY. 


ing  summary  is  made  from  data  obtained  by  analysis  and 
distillation  of  twenty-two  different  samples  of  crude  shale 
oil'7. 


Specific 
Gravity 

Average 

65°C 

Gasoline   to  150°C  

.750  —    .850 

11.7% 

Kerosene    to   300  °C    

.820  —    .900 

38% 

Heavy  oil    residue      .... 

900  —  1.02 

45% 

63% 

Unsaturated  hydrocarbons  in  crude  shale  oil 

80% 

Asphalt  in  crude  shale  oil 

2.5% 

Paraffin  in  crude  shale  oil 

5  0% 

Sulphur  in  crude  shale  oil 

75% 

Nitrogen  in  crude  shale  oil  

1.2% 

Black  Shale. 

"It  may  be  interesting  to  compare  with  this  table  the 
results  of  the  distillation  of  black  shale  from  eastern 
United  States,  where  extensive  beds  of  this  shale  are  known 
to  occur  directly  below  the  coal  measures.  Analyses  are 
by  the  United  States  Geological  Survey". 


State  — 

Number  of 
Samples 

Average 
Gallons  Oil 
Per  Ton 

Indiana               

7 

10 

Illinois       

2 

14 

3 

5.1 

Ohio                          

4 

7.1 

7 

27.6 

Tennessee                       

13 

5.2 

West  Virginia  

5 

1.4 

Canadian  Shales. 

"Oil  shales  in  Canada  are  quite  widespread  in  distri- 
bution and  have  been  investigated,  in  considerable  detail  by 
the  Canadian  Department  of  Mines.  The  most  important 
deposits  occur  in  New  Brunswick.  The  figures  below  are 
compiled  from  publications  'by  the  Canadian  Department 
of  Mines  and  the  United  States  Geological  Survey,  re- 
spectively : 


POPULAR    OIL    GEOLOGY. 

Average  Analyses  of  Oil  Shales. 


149 


Canadian 

U.  S. 

Number  of  samples  

44 

132 

Gallons  Oil  Per  Ton 

349 

19  2 

Specific  Gravity  of  Oil   

0.903 

0  918 

Degree  Beaume  of  Oil  

25 

252 

Pounds   Ammonium   Sulphate 
Per  Ton  

51.3 

16  0 

"The  greater  richness  of  the  Canadian  Shales  is  forc- 
ibly brought  out  in  this  table.  The  discrepancy  in  the 
Ammonium  Sulphate  content  is  especially  important  be- 
cause it  represents  the  most  valuable  constituent  of  oil 
shale". 

Other  Foreign  Countries. 

"Oil  shale  has  been  retorted  on  a  commercial  scale  in 
France  and  New  South  Wales  for  a  number  of  years,  but 
at  the  present  time  this  industry  is  declining". 
Scotland. 

"The  following  table  cited  from  a  paper  by  Egloff, 
gives  the  products  and  yields  of  3,500,000  tons  of  shale 
treated  in  Scotland  in  1916". 

Products  Marketed  from  Scottish  Oil  Shales,  1916. 
Total  Tons  Shale,  3,500,000. 


Gallons 

Per  Cent  of 
Oil  Yield 

Spec. 
Gravity 

Degree 
Beaum6 

Crude  Oil 

80  500  000 

091 

00    0 

'GOO  ooo 

0  7 

0  74 

cq  o 

Naphtha        

4  840'000 

5  1 

0  78 

49  5 

Burning  Oil  
Gas  or  Fuel  Oil 

22,000,000 
1  3  000  000 

oo   r 

Lt  O.  D 

16  2 

0.82 
0  86 

40.7 

00    0 

Lubricating   Oils    • 

11  000  000 

13  7 

0  90 

25  5 

Paraffin  Wax  (tons)  

27  500 

1  0 

110°-132° 

Coke  (tons)        

84,000 

3  0 

»  •  . 

Ammonium  Sulphate  (tons)  . 
Ammonia    (tons)    

59,400 
16,000 

1.41% 
per  ton 
shale 

0  44% 

per  ton 
shale 

150 


POPULAR    OIL    GEOLOGY. 


Figure  57.     Expei 


lental  oil  shale  retort  erected  to  test 
Colorado  shale. 

(Courtesy  D.  &  R.  G.  R.  R.) 


POPULAR  OIL  GEOLOGY.  151 

Methods  of  Treatment. 

The  first  commercial  plants  for  the  utilization  of  oil 
shale  were  erected  in  Scotland  in  1848.  Since  that  time 
they  have  been  in  continued  and  successful  operation.  The 
development  of  the  industry  has  been  carried  out  with 
much  skill.  The  methods  of  treatment  evolved  and  the 
machinery  employed  are  the  results  of  many  years  of 
practical  experience  -and  of  the  application  of  the  best 
scientific  and  technical  talent  procurable.  It  is  not  sur- 
prising, therefore,  to  find  the  Scottish  Shale  Oil  Industry 
flourishing  and  highly  successful. 

Scottish  Oil  Shale  Plants. 

A  Scottish  shale  oil  plant  is  quite  elaborate  and  con- 
sists really  of  two  separate  plants;  a  crude  oil  works  and 
a  refinery. 

Crude  Oil  Works. 

The  crude  oil  plants  are  usually  located  at  the  mine, 
as  it  is  cheaper  to  treat  the  shale  there  than  to  transport 
it  for  any  great  distance.  The  crude  oil  from  several 
plants  goes  to  a  single,  centrally  located  refinery.  The 
crude  oil  works  consist  of  retorts,  oil  condensers,  scrubbers, 
a  naphtha  plant,  and  an  ammonium  sulphate  plant. 

Retorts. 

Forty-four  to  sixty-six  retorts  are  arranged  in  bat- 
teries or  "benches".  In  these  the  shale  is  heated  and  dis- 
tilled. The  two  most  common  retorts  used  are  known  as 
the  Henderson  and  the  Pumpherston  or  Bryson  type.  The 
retorts  in  either  case  consist  of  two  parts — the  upper  and 
shorter  part  is  cast  iron;  the  lower  part,  firebrick.  They 
are  jacketed  by  flues  and  heated  to  a  temperature  of  about 
1,000°  C.  near  the  bottom  of  the  brick  part.  The  tempera- 
ture decreases  gradually  to  about  670°  C.  in  the  metal  part. 
Sufficient  dry  gas  is  yielded  in  the  distillation  of  the 


152 


POPULAR    OIL    GEOLOGY. 


Scottish  shales  to  furnish  all  the  fuel  required.  In  neither 
of  these  furnaces  is  the  shale  column  permitted  to  remain 
at  rest,  because  of  the  danger  of  melting  the  shale  and 
clogging  the  retort.  The  Henderson  retort  has  toothed 
rollers  at  the  bottom  which  support  the  shale  column  and 


Figure  58.     Oil  shale  retorts.     Henderson  type  at  left, 
Pumpherston  type  at  right. 

which  are  rotated  to  maintain  a  downward  movement  and 
to  discharge  the  spent  shales  at  the  bottom.  In  the  Bryson 
type,  the  shale  is  supported  by  a  table  provided  with  a  re- 
volving arm  which  keeps  the  shale  column  in  motion  and 
removes  the  shale  by  revolving  at  regular  intervals.  In 


POPULAR    OIL    GEOLOGY. 


154 


POPULAR    OIL    GEOLOGY. 


nearly  every  distillation  process  steam  is  introduced  into 
the  shale  at  the  bottom  of  the  furnace.  This  assists  in 
the  easy  and  complete  removal  of  the  oil  obtained,  combines 
with  the  nitrogen  in  the  shale  to  form  ammonia,  and  also 
combines  with  the  carbon  to  form  gases,  such  as  carbon 
monoxide  and  carbon  dioxide. 

Condensers  and  Separators. 

The  oil  and  the  gases  that  are  driven  off,  as  a  result 
of  the  distillation,  escape  through  outlet  pipes  near  the 
top  of  the  iron  section  of  the  retorts  and  are  conducted 
into  the  condensers.  These  are  huge  racks  or  coils  of  four 


Figure  60.     Bench  of  shale  retorts,  Broxburn,  Scotland. 
(Courtesy  Canada  Dept.  of  Mines) 


POPULAR  OIL  GEOLOGY.  155 

inch  iron  pipe  similar  in  shape  to  steam  heat  radiators. 
The  gases  are  cooled  to  air  temperature  in  these  and  the 
oil  and  water  is  condensed  and  drawn  off  into  separators. 
The  greater  part  of  the  ammonia  is  condensed  with  the 
water.  The  ammonia  water  goes  from  the  separator  to  the 
ammonium  sulphate  plant;  the  crude  oil  is  sent  to  the 
refinery. 

Scrubbers. 

The  uncondensable  gases  coming  from  the  separators 
still  contain  valuable  quantities  of  ammonia  and  of  naph- 
tha. These  are  washed  out  in  so-called  ascrubbing  towers"  ; 
the  ammonia  in  a  "water  scrubber" ;  the  naphtha  in  an  "oil 
scrubber".  Both  are  tall  towers  in  which  the  gases  are 
washed  with  a  fine  spray  of  water  or  of  oil,  respectively. 
The  washed  gases  eventually  obtained  are  used  as  fuel  to 
heat  the  retorts. 

Shale  Oil  Refineries. 

"Shale  oil  refineries  consist  of  (a)  stills  for  distilling 
the  crude  oil  and  refining  the  fractions;  (b)  agitators  and 
settling  tanks,  in  which  the  oils  are  treated  with  sulphuric 
acid  and  caustic  soda  for  the  separation  of  the  tarry  mat- 
ters; (c)  paraffin-house,  where  the  heavy  oil  obtained  from 
the  crude  oil  is  cooled  and  pressed  for  the  separation  of 
the  paraffin  wax;  (d)  paraffin  refinery,  where  the  wax  is 
refined;  (e)  stock  tanks  for  the  finished  products;  (f) 
shipping  department,  where  the  barrels  are  made  and  the 
products  are  shipped  to  the  consumers;  (g)  candle-house, 
where  the  paraffin  is  made  into  candles  for  the  trade ;  and 
sometimes  (h)  a  sulphuric  acid  manufactory,  where  the 
sulphuric  acid  required  for  refining  and  the  production 
of  ammonium  sulphate  is  made.  There  are  also,  of  course, 
shops,  sawmills,  offices,  and  laboratories.  All  are  ar- 
ranged with  clue  regard  to  convenience,  cheapness,  and 
safety  from  fire." 

The  various  refining  operations  cannot  be  described 
in  detail  here.  For  a  full  discussion  of  these,  the  more 


156 


POPULAR    OIL    GEOLOGY. 


POPULAR  OIL  GEOLOGY.  157 

elaborate  technical  treatises  should  be  consulted.*    The  fol- 
lowing products  are  yielded : 

1.  Permanent  gases;  used  as  fuel. 

2.  Shale  naphtha,  gasoline,  motor  spirits,  and 

illuminating  oil. 

3.  Lamp  oils  of  high  quality. 

4.  Intermediate  oils ;  used  for  the  manufacture 

of  gas  of  high  illuminating  power. 

5.  Lubricating  oils;  these  do  not  decrease  in 

viscosity   as   rapidly   as   other  mineral 
oils. 

0.     Paraffin;   candles,  waterproofing,   and  insu- 
lating. 

7.  Still  grease;  very  heavy  distillate,  used  for 

grease  making. 

8.  Still  coke ;  used  for  fuel. 

9.  Ammonium  sulphate;  used  for  fertilizer. 
10.     Fuel   oils;    tars,   residues,    and   dregs   unfit 

for  other  purposes. 

Future  of  Western  Oil  Shales. 

There  has  been  a  great  deal  of  newspaper  advertising 
and  propaganda  in  connection  with  oil  shale  enterprises. 
A  number  of  companies  have  been  organized  as  stock  sell- 
ing propositions,  rather  than  to  assist  in  the  development 
and  upbuilding  of  a  permanent  industry.  The  oil  shale 
industry  is  a  business  for  the  future.  Under  present  con- 
ditions, it  cannot  hope  to  compete  with  the  petroleum  in- 
dustry. The  energy  and  money  of  the  people  interested  in 
oil  shale  should  be  devoted  to  the  encouragement  of  scien- 
tific investigations  and  technical  research.  This  alone  can 
furnish  a  sound  basis  upon  which  there  can  be  a  healthy 
development  of  the  Oil  Shale  Industry. 

Very  little  is  definitely  known  of  such  features  as  th^ 
quantity  of  oil  yield,  the  quality  of  oil  yield,  the  proper- 

*  Bacon  and  Hamor,  "The  American  Petroleum  Industry,"  Vol.  II. 


158  POPULAR  OIL  GEOLOGY. 

tion  of  gas,  the  proportion  of  by-products  as  influenced  by 
the  type  of  furnace  used,  by  the  temperature  of  distillation, 
by  the  rate  of  distillation,  and  by  the  pressure  of  water  or 
steam.  For  Scotch  practice,  some  of  the  above  data  are 
available,  but  the  differences  in  labor  conditions,  in  trans- 
portation and  marketing  facilities,  and  other  economic  con- 
siderations make  it  improbable  that  the  Scottish  practice 
can  be  followed  successfully  in  the  exploitation  of  Ameri- 
can Oil  Shales.  The  data  enumerated  above  must  be  stud- 
ied in  the  light  of  American  conditions  and  requirements. 

Considering  the  present  lack  of  knowledge  of  the  fun- 
damentals of  oil  shale  refining,  it  must  be  apparent  that 
estimates  on  the  cost  of  commercial  shale  plants,  on  the 
cost  of  treatment  per  ton  of  shale,  on  the  value  of  the  prod- 
ucts yielded,  and  on  the  possible  profit  per  ton  cannot  be 
more  than  an  expression  of  personal  opinion,  and  had  prob- 
ably be  best  designated  as  a  guess.  The  oil  shale  industry 
must  develop  as  a  large  scale  manufacturing  enterprise, 
similar  to  the  manufacture  of  shoes.  In  the  shoe  industry, 
the  salient  factors  necessary  to  design,  build,  equip,  and 
manage  a  plant  have  been  established  by  continuous  prac- 
tice and  research;  in  the  oil  shale  industry,  they  are  as  yet 
unknown.  They  can  be  determined  by  technical  and  scien- 
tific investigations  more  accurately  and  much  more  cheaply 
than  by  the  construction  of  plants  designed  on  a  basis  of 
persgnal  opinion  and  preconceived  notions. 

The  following  important  facts  regarding  the  oil  shale 
situation  are  worth  emphasizing: 

1.  There  are  no  plants  operating  commercially  in 
the  United  States  at  this  time.  (January,  1920.) 

2.  The  cost  of  installation  of  a  commercial  plant  is 
problematical.       Estimates     range    from     $1,000,000     to 
$5,000,000. 

3.  Nothing  definite  is  known  about  the  costs  of  oil 
shale  operations,  or  the  possible  profits  to  be  derived  there- 
from. 


POPULAR  OIL  GEOLOGY.  159 

4.  Shale  oil  cannot  be  refined  in  the  ordinary  petro- 
leum refinery.     Shale  oil  is  an  exceedingly  complex  mix- 
ture, much  more  difficult  and  more  costly  ta  refine  thaTi 
petroleum. 

5.  The  development  of  the  Oil  Shale  Industry  on  a 
commercially  important  scale  will  require  many  years.     In 
the  immediate  future,  it  cannot  hope  to  compete  with  the 
petroleum  industry. 


XIV.   Oil  Investments 


In  the  purchase  of  oil  stocks  one  of  two  purposes  may 
actuate  the  buyer — either  speculation  or  investment.  As  a 
matter  of  fact,  the  element  of  risk  is  so  large  in  the  average 
oil  stock  that  many  people  refuse  to  consider  their  pur- 
chase a  really  legitimate  investment.  This  is  especially 
true  when  compared  with  an  investment  in  railroad  or  simi- 
lar bonds  or  real  estate,  all  of  which  have  a  fixed  value 
determined  by  the  annual  income  derived  from  them.  Oil 
property,  on  the  other  hand,  has  not  a  fixed  but  a  con- 
tinually decreasing  value.  Annual  dividends  paid  on  oil 
stocks  are  not  true  income  on  the  capital  invested,  but 
include  repayments  of  the  capital  in  small  installments. 
The  value  of  an  oil  stock,  similar  to  that  of  a  mining  stock, 
is  determined  by  the  sum  total  of  the  dividends  and  the 
length  of  time  necessary  to  obtain  them.  Oil  is  a  "wast- 
ing asset  which  is  always  in  process  of  distribution." 
When  the  oil  is  gone  the  payments  of  annual  dividends 
cease. 

Dividends  on  Oil  Stocks. 

One  of  the  most  important  ideas  to  carry  in  mind 
with  respect  to  oil  investments  is  the  fact  that  annual  divi- 
dends include  repayments  of  the  original  investment.  Any 
oil  property  should  repay  the  capital  within  three  to  five 
years ;  subsequent  payments,  therefore,  represent  dividends 
only.  When  this  fact  is  impressed  on  the  mind  of  the 
investor,  the  high  annual  dividends  paid  on  oil  stocks  will 
lose  much  of  their  attractiveness.  An  oil  stock  yielding 
twenty-six  per  cent  annual  dividends  must  continue  to  pro- 
duce at  the  same  rate  for  nearly  five  years  in  order  to 
assure  repayment  of  the  initial  investment  and  a  return 
of  six  per  cent  profit.  Many  oil  pools  are  completely 
drained  within  that  time. 

160 


POPULAR  OIL  GEOLOGY.  161 

Types  of  Oil  Investments. 

« 
Oil  investments  fall  under  one  of  three  heads : 

(a)  Investment    in    stocks    of   producing   con- 

cerns. 

(b)  Investment    in    stocks    of/  concerns    that 

intend  to  develop  territory  in  proven 
fields. 

(c)  Prospecting  or  "Wildcatting"  ventures  in 

territory  not  productive. 

These  are  ranked  according  to  the  safety  of  the  in- 
vestment, other  things  being  equal. 

Wildcatting. 

Prospecting  new  and  as  yet  unproductive  territory 
is  to  be  classed  mainly  under  the  head  of  speculation.  By 
far  the  majority  of  small  oil  companies  are  organized  for 
this  purpose.  Prospecting  ventures,  if  successful,  result 
in  fabulous  profits,  and  consequently  are  especially  attrac- 
tive. It  is  well  to  carry  in  mind  the  fact  that  while  there 
are  still  many  opportunities  of  finding  new  fields,  the 
chances  are  preponderantly  against  success.  The  field 
manager  of  one  of  the  larger  producing  companies  in 
America  is  authority  for  the  statement  that  in  wildcatting 
only  one  well  in  thirty-seven  proves  a  producer.  The  ele- 
ment of  risk  can  be  greatly  reduced  by  distributing  the 
investment  over  a  number  of  wildcat  areas.  The  investor 
should,  however,  satisfy  himself  that  the  properties  in 
question  have  been  investigated  by  a  reliable  and  thor- 
oughly competent  geologist,  and  that  their  drilling  has  been 
recommended. 

Geology  in  Wildcatting. 

The  following  editorial  from  "The  Mining  American" 
is  timely  and  to  the  point : 

"We  find  that  the  scramble  for  oil  lands  has,  in  some 
instances,  been  carried  to  irrational  limits.  Com- 
panies have  been  formed  upon  holdings  in  which, 
from  the  geologist's  viewpoint,  no  oil  could  possibly  be 


162  POPULAR  OIL  GEOLOGY. 

stored.  Expenditure  of  money  in  locating,  validating, 
and  drilling  of  such  lands  is  positively  reckless  and 
it  is  done  without — or  contrary  to — the  advice  of 
competent  experts.  Doings  of  this  sort  have  naught 
but  failure  ahead  and  they  lower  the  public's  faith 
in  the  state  and  in  the  industry. 

"Would  that  some  way  might  be  devised  and  put 
into  effect  to  prevent  such  fiascos.  There  are  enough 
really  good  oil  structures  in  Wyoming  to  go  'round 
among  legitimate  promoters.  Why  will  men  not 
limit  their  holdings  and  expenditures  to  them  ? 

"We  have  heretofore  dwelt  upon  the  advisability  of 
employing  petroleum  geologists  when  wildcatting. 
The  finding  of  oil  was  formerly  a  wild  gamble.  Now- 
adays it  need  not  be.  During  the  exploitation  of  the 
older  American  fields,  the  ratio  of  productive  wells 
to  all  wells  drilled  was  very,  very  small;  but  science 
has  studied  petroleum's  genesis  and  occurrence,  and 
theories  have  been  evolved  and  tested  in  practice  by 
skilled,  educated  men  until  the  factor  of  uncertainty 
in  drilling  for  natural  oil  has  been  radically  reduced 
and  is  becoming  smaller  all  the  time. 

"This  is  one  of  our  latest  technical  branches.  It 
is  thoroughly  recognized  by  every  large,  successful  oil 
company.  A  few  years  ago,  during  the  wildcatting 
of  fields  in  Kansas  and  Oklahoma,  success  in  bringing 
in  oil  wells  was  considerably  less  than  one  per  cent. 
Now,  with  scientific  guidance  available,  the  average 
is  around  sixty-eight  per  cent — and  it  would  be  still 
higher  if  it  were  not  that  some  concerns  still  consider 
it  economy  to  curtail  the  geologist's  fee  or  salary. 
False  economy!" 

The  wild  and  irrational  scramble  to  get  into  the  oil 
game  is  also  well  illustrated  in  the  number  of  new  oil  com- 
panies organized.  The  statement  has  been  made  on  good 
authority  that  the  combined  capitalization  of  the  com- 
panies operating  in  Wyoming  and  in  Colorado,  or  organized 
for  that  purpose  within  the  past  two  years,  is  so  great  that 


POPULAR  OIL  GEOLOGY.  163 

the  petroleum  production  of  the  entire  United  States  for 
1917  is  only  sufficient  to  pay  three  per  cent  interest  on  the 
capital,  without  providing  in  any  way  for  the  ultiniate 
return  of  the  money  invested. 

Producing  Companies. 

Risks  can  be  eliminated  largely  in  investments  in  the 
stock  of  companies  which  have  a  definite  production  es- 
tablished. In  this  particular  case  we  can  determine  the 
following  points : 

1.  Productive  capacity. 

2.  Cost  of  production  and  maintenance. 

3.  The  value  of  the  oil. 

4.  Location  and  market  facilities. 

5.  Financial  status  of  the  Company. 

Productive  Capacity. 

The  productive  capacity  of  a  particular  tract  of  ground 
can  be  determined  from  the  area  actually  oil-bearing,  and 
the  number  and  thickness  of  the  oil  sands  and  their  degree 
of  effective  saturation.  Wells  actually  drilled  on  the 
property  or  on  surrounding  properties,  studied  in  connec- 
tion with  the  structure  map  of  the  field,  will  give  much  of 
the  information  needed.  Producing  wells  on  adjacent 
properties  and  on  similar  structures  indicate  the  length 
of  life  and  tne  rate  of  decline  in  production  to  be  expected 
on  the  area  in  question. 

Cost  of  Maintenance  and  Production. 

Under  cost  of  maintenance  and  production  we  include 
the  drilling  of  wells,  cost  of  pumps,  pipe  lines,  storage 
tanks,  power  plants,  wages,  and  similar  expenditures. 
Again,  the  experience  in  adjacent  properties,  if  available, 
furnishes  valuable  information,  feuch  as  the  cost  of  drilling 
wells  and  of  maintaining  them  in  good  condition,  and  the 
number  of  wells  necessary  to  maintain  production  at  a 
definite  figure. 


164:  POPULAR    OIL    GEOLOGY. 

Value  of  Oil. 

The  value  of  oil  is  subject  to  extreme  variation.  This 
is  shown  by  the  diagram  in  figure  2,  page  3.  For  purposes 
of  estimating  the  value  of  property,  the  minimum  price 
paid  for  oil  should  be  used. 


/ooo 


/oo 

2OtOOC 


9000 


01 


/O 


3O        3-ST 
7~/'me,    //7  Months 


60 


Figure  62.     Typical  curves  showing  decline  in  production  of 

typical  wells.     Figures  at  left  show  initial  daily 

production  in  barrels. 

Location. 

Market  facilities,  accessibility  to  railroads  or  pipe 
lines,  and  to  refineries  are  features  worthy  of  serious  con- 
sideration. An  unfavorable  location  with  respect  to  these 
features  may  make  an  otherwise  promising  tract  unattrac- 
tive to  the  investor.  \7ery  few  oil  companies  rely  on 


POPULAR  OIL  GEOLOGY.  165 

production  from  a  single  field  alone,  but  have  areas  scat- 
tered over  a  number  of  different  structures  and  perhaps 
different  states.  This  distribution  of  risk  makes  their 
stock  more  attractive  to  the  investor,  and,  in  many  cases, 
puts  it  in  a  class  with  high  class  industrial  stocks  as  far 
as  security  is  concerned. 

Financial  Status  of  the  Company. 

Investment  in  the  stock  of  oil  companies  is  not  advis- 
able unless  the  investor  has  absolute  confidence  in  the  hon- 
esty and  integrity  of  the  management,  and  in  its  financial 
and  technical  ability. 

Hammond's  Don'ts. 

In  this  connection  I  cannot  do  better  than  to  quote 
John  Hays  Hammond's  rules  for  investors  in  Mining 
Stocks,  as  with  the  substitution  of  the  word  Oil  for  Mine 
these  are  applicable  and  to  the  point : 

First — Don't  invest  your  money  in  an  oil  property 
simply  because  of  the  fact  that  a  friend  of  yours  became 
rich  through  a  fortunate  investment  made  in  oil  stocks. 

Second — Don't,  on  the  other  hand,  be  deterred  from 
investing  in  an  oil  property  because  another  less  fortunate 
friend  became  bankrupt  through  some  other  oil  investment. 

Third — Don't  allow  any  insinuating,  slick,  dishonest, 
•  not  to  employ  the  short  and  uglier  word,  promoter,  or  so 
called  stock  broker,  to  overcome  your  natural  modesty  and 
convince  you  that,  because  you  have  been  successful  in  your 
own  line  of  business,  you  yourself  are  competent  to  deter- 
mine the  value  of  an  oil  property.  Many  men  of  business 
ability  in  their  own  lines  have  made  trips  of  self-deception 
to  see  for  themselves  that  which  existed  only  in  their 
imaginations.  " Shoemaker,  stick  to  your  last". 

Fourth — Don't  be  influenced  in  your  desire  to  pur- 
chase oil  stocks  by  a  bottle  of  oil  that  the  property  has 
produced,  even  though  you  yourself  have  seen  the  oil 
actually  on  the  ground.  This  is  similar  to  specimen  rock  in 
a  mine,  which  is  not  a  criterion  of  the  average  grade  of  the 
ore  upon  which  the  success  of  the  mine  depends.  I  remem- 


166  POPULAR  OIL  GEOLOGY. 

ber  the  story  of  old  John  Cashweiler,  a  well-known  mining 
capitalist  of  his  day,  when  he  was  asked  his  opinion  on  the 
value  of  a  property  from  which  very  rich  specimens  of  ore 
were  shown  him.  "You  might  as  well  show  me  the  hair 
from  the  tail  of  a  horse",  said  Cashweiler,  "and  then  ask 
me  how  fast  the  horse  can  trot." 

Fifth — Do  not  buy  stock  in  an  oil  property  because  it 
has  produced  a  profit  of  millions  "of  dollars  in  the  past, 
for  the  property  is  obviously  so  much  poorer  for  the  mil- 
lions already  abstracted. 

Sixth — Do  not  buy  stock  in  an"  oil  company  simply 
because  of  the  fact  that  its  property  adjoins  another  oil 
property  of  great  value.  That 'may  be  interesting,  but  it 
is  not  conclusive  as  to  the  value  of  the  property  in  question. 

Seventh — Do  not  buy  stock  in  an  oil  property  solely 
because  it  is  in  a  far-off  country,  even  though  distance  lends 
enchantment  to  the  view. 

Eighth — Above  all,  don't  buy  shares  in  an  oil  property 
unless  you  have  the  unqualifiedly  favorable  report  made 
by  an  oil  expert  of  known  integrity,  ability,  and  experience, 
and  one  who  has  made  a  success  in  investment  of  money  for 
his  clients.  An  engineer  may  have  the  best  obtainable 
technical  training,  supplemented  by  considerable  practical 
experience,  and  yet  lack  the  certain  qualifications  in  his 
professional  make-up  that  determine  success  or  failure. 

Ninth — Don't  buy  stock  in  an  oil  property  unless  you 
are  sure  that  the  board  of  directors  are  honest  and  com- 
petent, because  good  management  is  just  as  essential  to  suc- 
cess in  oil  production  as  it  is  in  other  enterprises. 

Tenth — In  short,  don't  abandon  all  your  good  common 
sense  just  because  the  investment  happens  to  be  one  in  oil 
and  not  in  some  other  class  of  industrial  securities. 


Ind 


ex 


A  Page 

Absaroka  fault 115 

Acetylene    15 

Accumulation,  Laws  of 76 

Age  of  oil 34 

Analyses  of  Oil  Shales 146 

Animal    remains,    Preserva- 
tion of,  as  fossils 44 

Anthracene    15 

Anticlinal  theory    76 

Anticlinal    theory    modifica- 
tions : 78 

Anticline,  arrested   94 

Anticlines    55 

Antiquity,  Uses  of  petro- 
leum in  5 

Appalachian,  Exhaustion  of, 

oil  field 2 

Aromatic  hydrocarbons 15 

Asphalt  base 17 

Asphalt  sealed  sands 96 

Atoms    14 

B 

Basin  folds   57 

Big  Muddy  oil  field 94 

Bituminous  rocks   24 

Black  Shale    147 

Boulder  oil  field 107 

Bryson  retort  150 

Buttes    .  .   39 


California,  Exhaustion  of, 

oil  fields  2 

Canadian  shales    148 

Capillary  attraction  71 

Carbide  theory 27 

Carboniferous  rocks  ..        ..105 


Page 

Casing  head  Gas 16 

Centroclinal  folds 57 

Chapopote   24 

Characteristics     of     forma- 
tion     123 

Coal  oil  industry 6 

Coal  theory   28 

Color  of  oil 23 

Colorado,  Eastern 107 

Colorado  Foothills   107 

Colorado,  Oil  fields  in 105 

Columnar  section   82 

Composition  of  natural  gas.  16 
Composition  of  petroleum..  17 

Compounds    11 

Condensers,    Shale   Oil 153 

Condensing  plants,  Gas....  16 

Conglomerates   37 

Contour  lines 80 

Convergence  sheet   85 

Correlation  of  rocks 41 

Cosmic  theory 'of  oil  origin.  25 

Cretaceous  rocks   105,  109 

Cross-bedding    .*.   38 

Crystalline  rocks   36 

D 

Dakota  sandstone 107 

De  Beque  oil  field 107 

Degree  Beaume  18 

Dip  and  strike 52 

Dip,  Effect  of,  on  flow  of  oil.138 
Displacement  along  faults. .  58 

Distillation  of  oils 21 

Distillation  test  of  oil 

shales 144,  145 

Distribution  of  oil  and  gas, 

Stratigraphic    49 


167 


168 


INDEX. 


Page 

Dividends    158 

Divining  rod    122 

Dolomites  as  reservoirs 66 

Domes 56,  90,  110,  114,  131 

Drake,  Col.  E.  L 7 

Driller's  classification  40 

Drilling,   deep    118 

Drilling  down  dip 120 

Drilling,   Offensive  methods 

in   138 

Dry  hole   131 

Dry  Natural  Gas 16 

Dual  theory  of  oil  origin...  29 

E 

Elements,  Chemical  11 

Embar  formation   105 

Erosion  forms  39 

Evolution,  Theory  of 42 

Exhaustion  of  oil  fields 2 

F 

Faults 57,  113,  114 

Florence  oil  field 105 

Folded  oil  fields 89 

Folding,  Degree  of 55 

Folding,  Nomenclature  of . .   56 

Folds   53 

Formation,  Geological 38 

Formation,  Processes  of  oil.  31 

Fossils    42 

Frontier  formation 105 

G 

Gas,  Casing  head 16 

Gas,  Composition  of 15 

Gas,  Condensing  plants....  16 

Gas,  Mineral  15 

Gas,  Natural  16 

Gas  pressure » . . . .  16,  70 

Gas,  Swamp   15 

Ge-anticline   112 

Geologic  maps  82 


Page 
Geologic  sections  in  the 

Rocky  Mountains  102 

Geological  Chronology  of 

North  America 46 

Geological  History  45 

Gilsonite  24 

Grahamite  24 

Green  River  formation.  120,  143 
Gushers  8 

H 

Hammond's  "Don'ts" 165 

Heat  gradient 71 

Henderson  retort    157 

Hogbacks    39 

Hydrocarbons,  Natural 14 


Igneous  Rocks   36 

Illinois,    Exhaustion    of,    oil 

field  2 

Indiana,   Exhaustion   of,   oil 

'   field 2 

Indications  of  oil 118,  121 

Investments    160 

Isochore  lines 84 

K 

Kansas,   Exhaustion   of,   oil 
fields   .  2 


Lake  asphalt   24 

Lander  oil  field 93 

Legal  status  130 

Lenticular  structure    96 

Limestones    37 

Limestones  as  reservoirs...   65 

Line  wells  140 

Lithological  conditions   ....124 
Location,    Effect   of,   on   oil 

property    164 

Lucas  Well  .  . .  113 


INDEX. 


169 


Page 


M 


Maintenance  of  oil  wells...  163 

Maltha  24 

Mancos  formation 107 

Marsh  gas  14 

Methane   14 

Mesaverde  formation 107 

Mesas 39 

Metamorphic  rocks 36 

Mexican  gushers *    8 

Migration,  Causes  of 69 

Migration,  Effect  of,  on  oil.   33 

Migration,  factors  74 

Mineral  gas    15 

Molecules 14 

Monoclinal  dip,  Oil  fields  of.  94 

Monocline    55 

Mowry  shale 105 

N 

Naphthalene   15 

Naphthene    . . .' 15 

Natural   gas    16 

Natural  gas,  Composition  of  17 

Natural  gas,   Dry 16 

Natural  gas,  Wet 16 

New  Mexico   110 

Nitrogen  in  gas 16 

Nitrogen  in  oil 17 

Normal  faults    .  .  57 


Odor  of  oil 23 

Offsetting  140 

Ohio,  Exhaustion  of,  oil 

fields  .- 2 

Oil,  Available  amount  of... 

137,  163 

Oil,  Flow  of 137 

Oil,  Indications  of 118 

Oil,  Value  of ..164 


Page 
Oil  and  gas,  Occurrence  of 

in  the  Rocky  Mountains..  102 
Oil   Company,   First  in  the 

United  States  7 

Oil  fields- 
Appalachian  2,  49,  61,  63 

California   17,  23,  49,  61, 

63,  90,  114 

Colorado. 21,  22,  49,  61,  90,  96 
Dutch  East  Indies.. 23,  50,  89 

Galicia   50,  61,  89 

Illinois 17,  49,  61 

India 89 

Indiana 23,  49,  61,  66,  94 

Kansas 16,  49,  61,  90 

Kentucky   116 

Louisiana  ...49,  61,  100,  113 
Mexico  ....8,  50,  61,  100,  114 

New  York  49,  61,  115 

Ohio 23,  49,  61,  66,  96, 

100,  112 

Oklahoma 49,  61,  63,  90, 

95,  116 

Pennsylvania  17,  95,  116 

Persia    66,  89 

Peru    50,  61,  89 

Roumania .....  50,    61,  89 

Russia 7,  8,  16,  50,  63,  89 

Texas 17,  23,  49,  61,  66, 

68,  100,  113 

Trinidad    24,  96 

West  Virginia 49,  61 

Wyoming..  17,  21,  22,  49,  61, 

90,  93,  97,  105,  115 

Oil  fields,  Classification  of . .   87 

Oil  formations 123 

Oil  migration 74 

Oil  seeps   118 

Oil  shale  refining,  Products 

of 157 

Oil  shales    .  ..120 


170 


INDEX. 


Page 
Oil  shales,  Utilization  of...  142 

Oil  showings 120 

Oil  springs,  Allegheny 

County,  New  York 6 

Oklahoma,  Exhaustion  of 

oil,  fields  2 

Olefine  15 

Open  sands  61 

Origin  of  oil 25 

Origin  of  oil,  Inorganic 

theories  of  25 

Origin  of  oil,  Organic 

theories  of  28 

Outcrops  41,  53 

Ozokerite  .  .  24 


Paraffin 14 

Paraffin  base  ' 17 

Petroleum,  Base  of 17 

Petroleum,  Composition  of.   17 

Pipe  lines,  First 7 

Plunging  fold 56 

Porosity  of  reservoirs 61 

Processes  of  oil  formation.  31 

Producing  oil   136 

Production,    Annual    United 

States   9 

Production,  cost  of 163 

Production,   United    States.     3 

Production,  World's 9 

Prospecting  for  oil 123 

Pumpherston  retort 151 


Rangely  oil  field 107 

Ravines,  Structural   95 

Refineries,  Shale  Oil 155 

Reservoirs  of  oil 61,  1X7 

Reservoirs,   Enclosing   beds 
of   .  .68 


Page 

Reservoirs  of  oil,  Shape  of.  64 
Residual  asphalt  or  paraffin. 120 

Retardation  Structures 127 

Retorts,  Oil  Shale 151 

Rise  of  Modern  Industry...     6 

Rock  Pressure  70 

Rocks,  Classification  of 36 

Rocks,  Marine  sedimentary.117 

Rocky  Mountain  fields 102, 

103,  104 

Russian  gushers   8 

Rusty  beds   105 

S 

Saline  domes   110 

Salt  Creek  oil  field 93 

Salt  water 119 

Salt  wells   6 

Sandstones    , 37 

Sandstones  as  reservoir 

rocks 61 

Scotland   49 

Scottish  oil  shale  plants...  151 

Scrubbers,  shale  oil 155 

Sedimentary  Rocks 36 

Separators,  Shale  Oil 154 

Shannon  sandstone    105 

Shales    37 

Shales  as  reservoirs 66 

Specific  gravity  as  cause  of 

migration 69 

Specific  gravity  of  oil 18 

Status,  Present  1 

Stratification    38 

Stratigraphic  distribution  of 

oil  and  gas  49 

Strike   52\ 

Structural  domes   100 

Structural  highs  90 

Structural   map    84,101 

Structural  section  ., 82 


INDEX. 


Page 

Structure    87 

Structures,  Type 125 

Sulphur  in  oil    18 

Supply,  United  States  avail- 
able         3 

Surface  tension  72 

Swamp  gas  , 15 

Synclines    55 

"   T 

Tank  steamers,  First 8 

Tensleep  sandstone  ; 105 

Terrace,  Structural 94 

Test  for  oil  in  sands 63 

Test  well,  Location  of 131 

Thermopolis  shale    105 

Thrust  faults   58 

Topographic  features  in  oil 

prospecting    127 

Topographic  maps    80 

Transitional  rocks   37 

Transportation   134 

Trap  structures 126 

Treatment  of  oil  shales, 

Methods  of 144,  151 

Trenton  limestone   110 

U 

Unconformities    60,  115 

United    States    annual    pro- 
duction  .  9 


Page 
United  States  available 

supply    3 

United  States  total  pro- 
duction     3 


Varieties  of  oil,  Causes  of . .  32 

Viscosity  of  oil  23 

Volcanic  domes  , ...  114 

W 

Wall  Creek  sandstone 105 

Wasatch  formation 107 

Water  pressure   70 

Wells,  Line 140 

Wells,  Maintenance  of 163 

Wells,  Spacing  of 136 

Wet  natural  gas   16 

White,  I.  C 4 

White  River  formation 107 

Wildcatting   161 

World's  production   9 

Wyoming — 

Big  Muddy  Field 95 

Lander  Oil  Field 94 

Oil  fields  in..- 105 

Oil  structures  in 98 

Salt  Creek  Field 94 

Shoshone  anticline 93 

Teapot  dome .94 


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